2024 JAMB Physics Past Questions — Part 2

Questions 64–125

64. 64.

    A body is whirled in a horizontal circle at the rate of 800 revolutions per minute. Determine the angular velocity

    1. A.100$\pi$rads$^{-1}$
    2. B.33.3$\pi$rads$^{-1}$
    3. C.29.5$\pi$rads$^{-1}$
    4. D.26.7$\pi$rads$^{-1}$

    Show answer

    Answer: D. 26.7$\pi$rads$^{-1}$

    AI explanation

    Analysis

    To solve this problem, we need to convert the frequency of rotation from "revolutions per minute" (rpm) to "radians per second" (rad/s), which is the standard unit for angular velocity ($\omega$).

    Concept

    Angular velocity ($\omega$) is defined as the rate of change of angular displacement. The relationship between angular velocity and frequency ($f$) is given by the formula:

    $\omega = 2\pi f$

    Where:

    • $f$ is the frequency in revolutions per second (Hz).
    • $\omega$ is the angular velocity in radians per second (rad/s).

    Step-by-Step Solution

    Step 1: Convert revolutions per minute to revolutions per second. The body completes 800 revolutions in 60 seconds (1 minute).

    $f = \frac{800 \text{ revolutions}}{60 \text{ seconds}}$

    $f = \frac{80}{6} \text{ rev/s}$

    $f = 13.33 \text{ rev/s}$

    Step 2: Calculate the angular velocity ($\omega$). Using the formula $\omega = 2\pi f$:

    $\omega = 2 \times \pi \times 13.33$

    $\omega = 26.66\pi \text{ rad/s}$

    Step 3: Round to the appropriate decimal place. Rounding $26.66\pi$ to one decimal place gives $26.7\pi \text{ rad/s}$.

    Conclusion

    Comparing our result to the given options, we find that $26.7\pi \text{ rad/s}$ matches option D.

    Exam Tip

    When dealing with rotational motion questions in JAMB, always check your units first! If the question gives you revolutions per minute, divide by 60 to get revolutions per second before multiplying by $2\pi$. If you forget to divide by 60, you will end up with a much larger number that will lead you to the wrong answer.

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65. 65.

    Photometer is used to measure

    1. A.Kinetic energy of liberated electrons
    2. B.Intensity of light
    3. C.frequency of light
    4. D.wavelength of light

    Show answer

    Answer: B. Intensity of light

    AI explanation

    Analysis of the Question

    The question asks for the specific function of a photometer in the context of physics. To answer this, we need to distinguish between instruments used for measuring light properties (intensity, wavelength, frequency) and those used for particle physics (like the photoelectric effect).

    Concept Explanation

    • Photometer: The word is derived from "photo" (light) and "meter" (measure). It is a scientific instrument used to measure the intensity of electromagnetic radiation, specifically visible light. It works by converting light energy into an electrical signal, which can then be measured.
    • Kinetic energy of electrons: This is typically measured using a retarding potential apparatus in experiments related to the photoelectric effect (often associated with Millikan’s experiment).
    • Frequency/Wavelength of light: These are usually measured using a spectrometer or an interferometer, which separates light into its component colors or measures the interference patterns of light waves.

    Step-by-Step Solution

    1. Define the instrument: A photometer is designed to quantify the strength or "brightness" of a light source at a specific point or over a surface.
    2. Evaluate the options: • A: Incorrect. Kinetic energy of electrons is related to the photoelectric effect, not photometry. • B: Correct. Photometry is defined as the science of the measurement of light in terms of its perceived brightness to the human eye, which is essentially the intensity of light. • C: Incorrect. Frequency is a property of the wave itself, usually measured via spectroscopy. • D: Incorrect. Wavelength is also a property of the wave, measured via diffraction or interference methods.

    Conclusion

    Based on the standard definition of optical instruments in Physics, a photometer is specifically used to measure the intensity of light.

    Exam Tip: When you see "meter" at the end of a physics term, think about what is being measured.

    • Photo-meter: Light intensity.
    • Spectro-meter: Spectrum (wavelength/frequency).
    • Galvano-meter: Small electric currents.
    • Calori-meter: Heat energy.

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66. 66.

    288KJ is conducted across two opposite faces of a 3m cube of temperature gradient 90ºCm$^{-1}$ in 7200s. Calculate the thermal conductivity.

    1. A.4.9 x 10$^{-2}$Wm$^{-1}$k$^{-1}$
    2. B.5.0 x 10$^{-2}$Wm$^{-1}$k$^{-1}$
    3. C.5.2 x 10$^{-2}$Wm$^{-1}$k$^{-1}$
    4. D.5.1 x 10$^{-2}$Wm$^{-1}$k$^{-1}$

    Show answer

    Answer: A. 4.9 x 10$^{-2}$Wm$^{-1}$k$^{-1}$

    AI explanation

    1. Analyze the Question

    We are asked to calculate the thermal conductivity ($k$) of a material given the following parameters:

    • Heat energy ($Q$) = $288\text{ kJ} = 288,000\text{ J}$
    • Side of the cube ($L$) = $3\text{ m}$
    • Temperature gradient ($\frac{\Delta\theta}{\Delta x}$) = $90^\circ\text{Cm}^{-1}$
    • Time ($t$) = $7,200\text{ s}$

    2. Explain the Concept

    The rate of heat transfer ($H$) through a material is given by the formula:

    $H = \frac{Q}{t} = kA \left( \frac{\Delta\theta}{\Delta x} \right)$

    Where:

    • $Q$ is the heat energy.
    • $t$ is the time.
    • $k$ is the thermal conductivity.
    • $A$ is the cross-sectional area.
    • $\frac{\Delta\theta}{\Delta x}$ is the temperature gradient.

    Since the object is a cube with side length $L = 3\text{ m}$, the area of one face is $A = L^2 = 3^2 = 9\text{ m}^2$.

    3. Show the Solution

    Step 1: Calculate the rate of heat flow ($H$)

    $H = \frac{Q}{t} = \frac{288,000\text{ J}}{7,200\text{ s}} = 40\text{ W}$

    Step 2: Rearrange the formula to solve for $k$

    $k = \frac{H}{A \times (\text{temperature gradient})}$

    Step 3: Substitute the values

    $k = \frac{40}{9 \times 90}$

    $k = \frac{40}{810}$

    $k \approx 0.04938\text{ Wm}^{-1}\text{K}^{-1}$

    Step 4: Convert to standard form

    $k \approx 4.938 \times 10^{-2}\text{ Wm}^{-1}\text{K}^{-1}$

    Rounding to two significant figures as presented in the options, we get $4.9 \times 10^{-2}\text{ Wm}^{-1}\text{K}^{-1}$.

    4. Identify the Answer

    Comparing our result with the given options, the correct value is A.

    5. Tip

    When dealing with thermal conductivity problems, always ensure your units are consistent. Convert kilojoules (kJ) to Joules (J) immediately, and remember that for a cube, the area $A$ is simply the square of the side length ($L^2$). If the temperature gradient is already given as a single value ($\frac{\Delta\theta}{\Delta x}$), do not divide by the length again!

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67. 67.

    The dimension of power is

    1. A.ML$^2$T$^{-3}$
    2. B.ML$^1$T$^2$
    3. C.ML$^2$T$^{-2}$
    4. D.MLT$^2$

    Show answer

    Answer: A. ML$^2$T$^{-3}$

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68. 68.

    An ideal transformer has

    1. A.Maximum primary resistance
    2. B.No flux leakage
    3. C.Hysteresis
    4. D.Eddy current

    Show answer

    Answer: B. No flux leakage

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69. 69.

    Calculate the power of an object which moves through a distance of 500cm in 1s on a frictionless surface by a horizontal force of 50N

    1. A.200W
    2. B.300W
    3. C.350W
    4. D.250W

    Show answer

    Answer: D. 250W

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70. 70.

    A mass of gas at 40mmHg is heated from 298k to 348k at constant volume. Cal the pressure exerted by the gas.

    1. A.50.21mmHg
    2. B.46.71mmHg
    3. C.42.35mmHg
    4. D.35.12mmHg

    Show answer

    Answer: B. 46.71mmHg

    AI explanation

    Analysis

    This problem involves the relationship between the pressure and temperature of a fixed mass of gas when the volume is kept constant. This is governed by Gay-Lussac’s Law (also known as the Pressure Law).

    Concept

    Gay-Lussac’s Law states that for a fixed mass of gas at constant volume, the pressure ($P$) is directly proportional to its absolute temperature ($T$):

    $P \propto T \quad \text{or} \quad \frac{P_1}{T_1} = \frac{P_2}{T_2}$

    Where:

    • $P_1$ = Initial pressure
    • $T_1$ = Initial temperature
    • $P_2$ = Final pressure
    • $T_2$ = Final temperature

    Solution

    Step 1: Identify the given values

    • $P_1 = 40 \text{ mmHg}$
    • $T_1 = 298 \text{ K}$
    • $T_2 = 348 \text{ K}$
    • $P_2 = ?$

    Step 2: Rearrange the formula to solve for $P_2$

    $\frac{P_1}{T_1} = \frac{P_2}{T_2}$

    $P_2 = \frac{P_1 \times T_2}{T_1}$

    Step 3: Substitute the values into the equation

    $P_2 = \frac{40 \times 348}{298}$

    $P_2 = \frac{13920}{298}$

    $P_2 \approx 46.7114 \text{ mmHg}$

    Rounding to two decimal places, we get 46.71 mmHg.

    Conclusion

    Comparing our result with the given options, the correct value is 46.71 mmHg.

    Exam Tip

    Always ensure your temperature is in Kelvin when using gas laws. If a question gives you temperature in Celsius, remember to add 273 to convert it to Kelvin before plugging it into your formula. Also, since pressure is directly proportional to temperature, if the temperature increases, your final pressure must be higher than the initial pressure. This helps you quickly eliminate impossible options!

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71. 71.

    The tangential force acting on an object that opposes it from sliding freely on the adjacent surface is called

    1. A.Normal force
    2. B.Friction force
    3. C.Weight
    4. D.Upthrust

    Show answer

    Answer: B. Friction force

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72. 72.

    An accumulator is 90% efficient. If it gives out 2700J of energy while discharging, how much energy does it take in?

    1. A.3600J
    2. B.3000J
    3. C.3200J
    4. D.2430J

    Show answer

    Answer: B. 3000J

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73. 73.

    When thermal energy in a solid is increased, the change in state is called

    1. A.melting
    2. B.evaporation
    3. C.freezing
    4. D.condensation

    Show answer

    Answer: A. melting

    AI explanation

    Analysis

    The question asks for the specific term used to describe the phase change that occurs when a solid substance absorbs thermal energy (heat) until it transitions into a liquid state.

    Concept Explanation

    In thermodynamics, matter exists in different states (solid, liquid, and gas). These states are determined by the kinetic energy of the molecules.

    • Solid: Molecules are tightly packed and vibrate in fixed positions.
    • Thermal Energy: When you add heat to a solid, the kinetic energy of the molecules increases, causing them to vibrate more vigorously.
    • Phase Change: Eventually, the energy becomes sufficient to overcome the intermolecular forces holding the solid structure together. The solid begins to lose its rigid shape and turns into a liquid. This process is known as melting (or fusion).

    Let's look at the other options to understand why they don't fit:

    • Evaporation: This is the change from a liquid to a gas.
    • Freezing: This is the change from a liquid to a solid (this happens when thermal energy is removed, not increased).
    • Condensation: This is the change from a gas to a liquid.

    Step-by-Step Solution

    1. Identify the starting state: The question specifies a "solid."
    2. Identify the process: The question specifies that thermal energy is "increased."
    3. Determine the result: Increasing the temperature of a solid leads to the breaking of its lattice structure, resulting in a liquid.
    4. Match with terminology: The scientific term for the transition from solid to liquid is melting.

    Conclusion

    Based on the principles of thermodynamics, when a solid is heated to its melting point, it undergoes a phase change into a liquid. Therefore, the correct term is melting.

    Exam Tip: Always remember the direction of heat flow. If heat is added, the substance moves "up" the energy scale (Solid → Liquid → Gas). If heat is removed, the substance moves "down" the energy scale (Gas → Liquid → Solid).

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74. 74.

    Which of the following is the best as shaving mirror?

    1. A.Concave mirror
    2. B.Convex mirror
    3. C.plane mirror
    4. D.parabolic mirror

    Show answer

    Answer: A. Concave mirror

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75. 75.

    A monochromatic light is one that

    1. A.can undergo dispersion
    2. B.cannot be refracted
    3. C.has one wavelength
    4. D.has many wavelength

    Show answer

    Answer: C. has one wavelength

    AI explanation

    Analysis

    The question asks for the definition of "monochromatic light." In physics, particularly in optics, the term is derived from Greek roots: mono (one) and chroma (color).

    Concept Explanation

    Light is an electromagnetic wave characterized by its wavelength ($\lambda$) and frequency ($f$).

    • Polychromatic light (like white light) is composed of many different wavelengths (colors) mixed together. When white light passes through a prism, it undergoes dispersion, splitting into its constituent colors (the visible spectrum).
    • Monochromatic light consists of light of a single, specific wavelength (or frequency). Because it has only one wavelength, it cannot be split further into other colors.

    Step-by-Step Solution

    1. Evaluate Option A: Monochromatic light cannot undergo dispersion because dispersion is the separation of light into its constituent wavelengths. Since monochromatic light has only one wavelength, there is nothing to separate.
    2. Evaluate Option B: Monochromatic light can definitely be refracted. Refraction occurs when light changes speed as it passes from one medium to another (e.g., from air to glass). This is the principle behind lenses and prisms.
    3. Evaluate Option C: By definition, "mono" means one. Therefore, monochromatic light is light that consists of a single wavelength.
    4. Evaluate Option D: This describes polychromatic light, not monochromatic light.

    Conclusion

    Based on the definition of monochromatic light, it is light characterized by a single wavelength.

    Exam Tip: Whenever you see the prefix "mono-" in science (like monohybrid in Biology or monochromatic in Physics), always associate it with the number one. This will help you quickly eliminate options that suggest multiple components.

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76. 76.This question needs a diagram, table or passage that we don't have yet, so it isn't shown.

77. 77.

    A thick glass tumbler cracks when boiling water is poured into it because

    1. A.The inside expands more rapidly than the outside
    2. B.The inside expands less rapidly than the outside
    3. C.The expansion is even
    4. D.It does not expand

    Show answer

    Answer: A. The inside expands more rapidly than the outside

    AI explanation

    Analysis

    This question tests your understanding of Thermal Expansion in solids, specifically how heat transfer affects materials with low thermal conductivity, like glass.

    Concept Explanation

    When you pour boiling water into a thick glass tumbler, you are introducing a high amount of thermal energy to the inner surface of the glass.

    1. Thermal Conductivity: Glass is a poor conductor of heat (an insulator). This means heat does not travel quickly from the inner surface to the outer surface.
    2. Differential Expansion: Because the inner surface is in direct contact with the boiling water, it heats up and expands almost immediately. However, because glass is a poor conductor, the outer surface remains relatively cool and does not expand at the same rate.
    3. Stress: The inner layer of the glass tries to expand, but it is being "held back" by the cooler, rigid outer layer. This creates a significant amount of internal stress (tension) within the glass. When this stress exceeds the strength of the glass, the material fractures, causing the tumbler to crack.

    Step-by-Step Solution

    • Step 1: Identify the physical process. The heat from the water causes the molecules on the inner wall of the glass to vibrate faster and move further apart (expansion).
    • Step 2: Consider the property of the material. Since glass is a poor conductor, the heat is trapped on the inside.
    • Step 3: Compare the layers. The inside layer expands rapidly due to the heat, while the outside layer remains at a lower temperature and maintains its original size.
    • Step 4: Conclusion. The mismatch in expansion rates between the inner and outer layers creates a strain that leads to the crack.

    Identifying the Answer

    Comparing our analysis to the options provided:

    • Option A correctly describes that the inside expands more rapidly than the outside.
    • Options B, C, and D are incorrect because they contradict the physical behavior of glass under rapid heating.

    Exam Tip

    Whenever you see questions about glass cracking due to temperature changes, remember the keyword: "Poor Thermal Conductivity." This is the reason why the heat doesn't distribute evenly, leading to the uneven expansion that causes the break.

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78. 78.

    The gravitational force between two objects is 10N, what is the new value of the force if the distance between them is halved?

    1. A.10N
    2. B.20N
    3. C.40N
    4. D.80N

    Show answer

    Answer: C. 40N

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79. 79.

    What is the colour of red rose under a blue light?

    1. A.Green
    2. B.Blue
    3. C.Yellow
    4. D.Black

    Show answer

    Answer: D. Black

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80. 80.

    Calculate the upthrust on a spherical ball of volume 4.2 x 10$^{-4}$m$^{3}$ when totally immersed in a liquid of density 1028kgm$^{-3}$

    1. A.5.2N
    2. B.4.3N
    3. C.3.0N
    4. D.2.4N

    Show answer

    Answer: B. 4.3N

    AI explanation

    1. Analyze the Question

    We are asked to calculate the upthrust (buoyant force) acting on a spherical ball that is completely submerged in a liquid.

    Given data:

    • Volume of the ball ($V$) = $4.2 \times 10^{-4} \, \text{m}^3$
    • Density of the liquid ($\rho$) = $1028 \, \text{kg/m}^3$
    • Acceleration due to gravity ($g$) = $9.8 \, \text{m/s}^2$ (standard constant used in JAMB Physics)

    2. Explain the Concept

    According to Archimedes' Principle, the upthrust on an object immersed in a fluid is equal to the weight of the fluid displaced by the object.

    The formula for upthrust ($U$) is:

    $U = V \times \rho \times g$

    Where:

    • $V$ is the volume of the displaced fluid (which is equal to the volume of the submerged object).
    • $\rho$ is the density of the fluid.
    • $g$ is the acceleration due to gravity.

    3. Show the Solution

    Substitute the given values into the formula:

    $U = (4.2 \times 10^{-4} \, \text{m}^3) \times (1028 \, \text{kg/m}^3) \times (9.8 \, \text{m/s}^2)$

    Step-by-step calculation:

    1. Multiply the volume by the density: $4.2 \times 1028 = 4317.6$ $4317.6 \times 10^{-4} = 0.43176$

    2. Multiply the result by gravity ($g = 9.8$): $0.43176 \times 9.8 = 4.231248 \, \text{N}$

    Rounding this to one decimal place, we get approximately 4.23 N. Looking at the provided options, 4.3 N is the closest value.

    4. Identify the Answer

    Comparing our result to the options provided: A. 5.2N B. 4.3N C. 3.0N D. 2.4N

    This is consistent with our calculation, as 4.23N rounds to 4.3N.

    5. Tip

    When solving buoyancy problems in JAMB, always ensure your units are in SI units (meters, kilograms, seconds). If the volume is given in $\text{cm}^3$, you must convert it to $\text{m}^3$ by multiplying by $10^{-6}$ before plugging it into the formula. Also, if the question doesn't specify $g$, always use $9.8 \, \text{m/s}^2$ or $10 \, \text{m/s}^2$ depending on which gives a result matching the options.

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81. 81.

    An example of a non-rechargeable cell is

    1. A.nickel iron
    2. B.mercury cadmium
    3. C.dry leclanche
    4. D.lead-acid

    Show answer

    Answer: C. dry leclanche

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82. 82.

    Newton's law of cooling is valid only for a

    1. A.small temperature range
    2. B.large temperature range
    3. C.free flow range
    4. D.presence of heat source

    Show answer

    Answer: A. small temperature range

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83. 83.

    A blacksmith heated a metal whose cubic expansivity  is 3.9 x 10$^{-6}$K$^{-1}$. Calculate the area expansivity.

    1. A.3.9 x 10$^{-6}$K$^{-1}$
    2. B.2.6 x 10$^{-6}$K$^{-1}$.
    3. C.1.3 x 10$^{-6}$K$^{-1}$.
    4. D.1.6 x 10$^{-6}$K$^{-1}$.

    Show answer

    Answer: B. 2.6 x 10$^{-6}$K$^{-1}$.

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84. 84.This question needs a diagram, table or passage that we don't have yet, so it isn't shown.

85. 85.

    According to kinetic theory of gases, the pressure exerted by the gas on the wall is equal

    1. A.change in momentum per unit volume
    2. B.rate of change of momentum imparted by the walls per second per unit area
    3. C.momentum imparted to the walls per unit area
    4. D.change in momentum imparted to the walls per unit area

    Show answer

    Answer: B. rate of change of momentum imparted by the walls per second per unit area

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86. 86.

    Bifocal lens is used to correct the eye defect of

    1. A.astigmatism
    2. B.hypermatropia
    3. C.myopia
    4. D.presbyopia

    Show answer

    Answer: D. presbyopia

    AI explanation

    Analysis

    The question asks for the specific eye defect that is corrected by the use of a bifocal lens. To answer this, we must understand the nature of common eye defects and the lenses used to treat them.

    Concept Explanation

    Eye defects occur when the eye's ability to focus light on the retina is impaired. Here is a breakdown of the common defects:

    1. Myopia (Short-sightedness): The person can see near objects clearly but distant objects appear blurred. It is corrected using a concave (diverging) lens.
    2. Hypermetropia (Long-sightedness): The person can see distant objects clearly but near objects appear blurred. It is corrected using a convex (converging) lens.
    3. Astigmatism: This occurs when the cornea or lens has an irregular curvature, causing blurred vision at all distances. It is corrected using cylindrical lenses.
    4. Presbyopia: This is an age-related condition where the eye loses its ability to focus on near objects due to the hardening of the lens. Because elderly people often suffer from both presbyopia (difficulty with near vision) and sometimes other distance vision issues, they require a lens that combines both convex and concave powers. This is known as a bifocal lens.

    Step-by-Step Solution

    • Step 1: Evaluate the function of a bifocal lens. A bifocal lens contains two parts: the upper part for distance vision and the lower part for reading (near vision).
    • Step 2: Match the defect to the lens. Since presbyopia involves the loss of near-focusing ability (often occurring alongside distance vision issues in older adults), the bifocal lens is the standard medical solution.
    • Step 3: Compare with other options. • Astigmatism requires cylindrical lenses. • Hypermetropia requires convex lenses. • Myopia requires concave lenses.
    • Step 4: Conclude that presbyopia is the correct match for bifocal lenses.

    Conclusion

    The correct option is D.

    Exam Tip

    To remember this easily, think of the word "Presbyopia" as the "old age" defect. When people get older, they often need "two" (bi-) focuses—one to look at the road while driving and one to read their newspaper. Hence, Bi-focal for Presbyopia.

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87. 87.

    The unit of impedance is

    1. A.$\Omega$
    2. B.T
    3. C.H
    4. D.W

    Show answer

    Answer: A. $\Omega$

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88. 88.

    The simple form of the lead acid accumulator often has a negative pole of

    1. A.Zinc perioxide
    2. B.Lead peroxide
    3. C.Sulphuric acid
    4. D.lead plate

    Show answer

    Answer: D. lead plate

    AI explanation

    Analysis

    This question tests your knowledge of the chemical components of a secondary cell, specifically the lead-acid accumulator, which is commonly used in vehicles. You need to identify the material used for the negative electrode (anode) during the discharge process.

    Concept Explanation

    A lead-acid accumulator consists of two plates immersed in an electrolyte of dilute sulphuric acid ($H_2SO_4$):

    1. Positive Plate (Cathode): Made of Lead (IV) oxide or Lead peroxide ($PbO_2$). This is usually brown in color.
    2. Negative Plate (Anode): Made of spongy metallic lead ($Pb$). This is usually grey in color.

    When the battery is in use (discharging), a chemical reaction occurs where the lead plate and the lead peroxide plate both react with the sulphuric acid to form lead (II) sulphate ($PbSO_4$).

    Step-by-Step Solution

    • Step 1: Identify the components of the lead-acid accumulator. The electrolyte is sulphuric acid.
    • Step 2: Distinguish between the electrodes. The positive electrode is Lead peroxide ($PbO_2$).
    • Step 3: Identify the negative electrode. The negative pole is composed of a porous or "spongy" lead plate.
    • Step 4: Compare with the options provided. • A is incorrect (Zinc is used in Leclanché cells). • B is the positive pole (Lead peroxide). • C is the electrolyte, not an electrode. • D matches our identification of the negative pole.

    Conclusion

    The negative pole of a lead-acid accumulator is made of a lead plate.

    Exam Tip: To remember this easily, think of the "P" in Positive and Peroxide. The positive plate is Lead Peroxide. Since the negative plate is the other one, it must be the plain Lead plate.

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89. 89.

    A practical application of total internal reflection is found in

    1. A.rainbow
    2. B.diverging lens
    3. C.converging lens
    4. D.fiber optics

    Show answer

    Answer: D. fiber optics

    AI explanation

    1. Analyze the question

    The question asks for a practical application of total internal reflection (TIR). We need to identify which of the given options relies on this specific optical phenomenon to function.

    2. Explain the concept

    Total Internal Reflection (TIR) occurs when light traveling from a denser medium to a less dense medium hits the boundary at an angle greater than the critical angle. Instead of refracting (passing through), the light is completely reflected back into the denser medium.

    For TIR to occur, two conditions must be met:

    1. Light must travel from a medium with a higher refractive index to one with a lower refractive index.
    2. The angle of incidence must be greater than the critical angle for the pair of media.

    3. Show the solution

    Let's evaluate the options:

    • A. Rainbow: This is primarily caused by the refraction, dispersion, and internal reflection of sunlight within water droplets. While internal reflection occurs, it is not the primary mechanism defined as "total internal reflection" in the context of fiber optics.
    • B & C. Diverging and Converging Lenses: These operate based on the principle of refraction. Light passes through the glass, bending according to Snell's Law to focus or spread light.
    • D. Fiber Optics: This is the classic application of TIR. A fiber optic cable consists of a core with a high refractive index surrounded by a cladding with a lower refractive index. Light signals enter the core and strike the boundary between the core and cladding at an angle greater than the critical angle. Consequently, the light is trapped inside the core and "bounces" along the length of the cable with minimal loss of signal.

    4. Identify the answer

    Based on the principles of optics, fiber optics is the most direct and well-known practical application of total internal reflection.

    Correct Option: D

    5. Exam Tip

    To remember the conditions for TIR, use the mnemonic "D-to-R, Angle-is-Greater":

    • D-to-R: Light must travel from a Denser medium to a Rarer medium.
    • Angle-is-Greater: The angle of incidence must be Greater than the critical angle.

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90. 90.

    In a Hare's apparatus, the height of water and a liquid X are 0.3m and 0.5m respectively. The relative density of x is?

    1. A.0.4
    2. B.0.6
    3. C.1.7
    4. D.2.0

    Show answer

    Answer: B. 0.6

    AI explanation

    1. Analyze the question

    We are given the heights of two liquids (water and liquid X) in a Hare's apparatus and asked to find the relative density of liquid X.

    2. Explain the concept

    A Hare's apparatus works on the principle of balancing pressure. Since both liquids are subjected to the same atmospheric pressure at the top of the tubes, the pressure exerted by the columns of liquid must be equal at the common level:

    $P_w = P_x$

    $\rho_w \cdot g \cdot h_w = \rho_x \cdot g \cdot h_x$

    Where:

    • $\rho_w$ = density of water
    • $\rho_x$ = density of liquid X
    • $h_w$ = height of water column
    • $h_x$ = height of liquid X column
    • $g$ = acceleration due to gravity (which cancels out)

    The relative density (or specific gravity) of a substance is defined as the ratio of its density to the density of water:

    $\text{Relative Density} = \frac{\rho_x}{\rho_w}$

    From our pressure equation, we can rearrange to find the ratio:

    $\frac{\rho_x}{\rho_w} = \frac{h_w}{h_x}$

    3. Show the solution

    • Given: • Height of water ($h_w$) = 0.3 m • Height of liquid X ($h_x$) = 0.5 m

    • Calculation: $$\text{Relative Density of X} = \frac{h_w}{h_x}$$ $$\text{Relative Density of X} = \frac{0.3}{0.5}$$ $$\text{Relative Density of X} = \frac{3}{5} = 0.6$$

    4. Identify the answer

    Comparing our result to the options provided, the correct value is 0.6. This matches option B.

    5. Tip

    In a Hare's apparatus, always remember the inverse relationship: the liquid with the greater height is the less dense liquid. Since the height of liquid X (0.5m) is greater than the height of water (0.3m), liquid X must be less dense than water (Relative Density < 1). This quick check helps you eliminate options C and D immediately!

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91. 91.

    Pilots uses aneroid barometer to know the height above sea level because

    1. A.Very accurate
    2. B.Small and convenient
    3. C.Heavy and huge
    4. D.Costly

    Show answer

    Answer: B. Small and convenient

    AI explanation

    Analysis

    The question asks for the primary reason why pilots prefer the aneroid barometer over other types of barometers (like the mercury barometer) for measuring altitude in an aircraft.

    Concept Explanation

    An aneroid barometer is a device used to measure atmospheric pressure without using any liquid. It consists of a flexible metal box (an aneroid cell) that expands or contracts as the external air pressure changes. This movement is transmitted through a mechanical linkage to a pointer on a dial.

    In aviation, this device is calibrated to read altitude instead of pressure, and it is known as an altimeter.

    • Mercury barometers are tall, fragile, and contain toxic liquid mercury, making them completely unsuitable for a moving aircraft.
    • Aneroid barometers are compact, portable, and do not rely on gravity to keep a liquid column level, which is essential when a plane is banking, climbing, or descending.

    Step-by-Step Solution

    1. Evaluate Option A: While aneroid barometers are useful, they are generally less accurate than mercury barometers, which are considered the standard for precision. Therefore, accuracy is not the main reason they are chosen for flight.
    2. Evaluate Option B: Because they are compact, lightweight, and contain no liquid, they are highly portable and convenient to install in the tight space of an aircraft cockpit. This makes them the practical choice for aviation.
    3. Evaluate Option C: Being "heavy and huge" would be a disadvantage for an aircraft, where weight reduction is a priority.
    4. Evaluate Option D: Cost is not the primary functional reason for their use in aviation; their physical suitability is.

    Conclusion

    The aneroid barometer is the standard choice for aircraft because its design is compact, robust, and does not require a liquid column, making it small and convenient for cockpit use.

    Exam Tip: Whenever you see questions about barometers in Physics, remember: Mercury = High accuracy but fragile/bulky; Aneroid = Portable, convenient, and ideal for mobile applications like aviation or mountain climbing.

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92. 92.

    If the displacement of a car is proportional to the square of time, then the car is moving with

    1. A.Uniform acceleration
    2. B.Uniform velocity
    3. C.Increasing acceleration
    4. D.Decreasing acceleration

    Show answer

    Answer: A. Uniform acceleration

    AI explanation

    Analysis

    The question asks us to determine the type of motion a car exhibits when its displacement ($s$) is directly proportional to the square of time ($t^2$).

    Concept

    In kinematics, we use the equations of motion to describe how displacement, velocity, and acceleration relate to time.

    • Displacement ($s$): The distance moved in a specific direction.
    • Velocity ($v$): The rate of change of displacement with respect to time ($v = \frac{ds}{dt}$).
    • Acceleration ($a$): The rate of change of velocity with respect to time ($a = \frac{dv}{dt}$).

    Step-by-Step Solution

    1. Translate the statement into a mathematical equation: We are told that displacement ($s$) is proportional to the square of time ($t^2$): $$s \propto t^2$$This can be written as:$$s = kt^2$$(where$k$ is a constant of proportionality).

    2. Find the velocity ($v$): Velocity is the first derivative of displacement with respect to time: $$v = \frac{ds}{dt} = \frac{d}{dt}(kt^2)$$ $$v = 2kt$$

    3. Find the acceleration ($a$): Acceleration is the derivative of velocity with respect to time: $$a = \frac{dv}{dt} = \frac{d}{dt}(2kt)$$ $$a = 2k$$

    4. Interpret the result: Since $k$ is a constant, $2k$ is also a constant. This means the acceleration of the car does not change over time. When acceleration is constant, we describe the motion as uniform acceleration.

    Conclusion

    Since the acceleration is constant ($a = 2k$), the car is moving with uniform acceleration.

    Exam Tip: Remember this simple hierarchy for motion:

    • If $s \propto t^0$ (constant), velocity is zero.
    • If $s \propto t^1$ (linear), velocity is constant (uniform velocity).
    • If $s \propto t^2$ (quadratic), acceleration is constant (uniform acceleration).

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93. 93.

    In voltage measurement, the potentiometer is preferred to voltmeter because it

    1. A.has a wider range
    2. B.consumes negligible current
    3. C.is bulky
    4. D.responds faster than voltmeter

    Show answer

    Answer: B. consumes negligible current

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94. 94.

    A sonometer's fundamental note is 50Hz, what is the new frequency when the tension is four times the original?

    1. A.25Hz
    2. B.100Hz
    3. C.200Hz
    4. D.250Hz

    Show answer

    Answer: B. 100Hz

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95. 95.

    Calculate the magnetic force on an electron in a magnetic field of flux density 10T, with a velocity of 3 x 10$^7$m/s at 60º to the magnetic field (e = 1.6 x 10$^{-19}$C)

    1. A.4.8 x 10$^{-11}$N
    2. B.4.6 x 10$^{-12}$N
    3. C.4.16 x 10$^{-11}$N
    4. D.4.3 x 10$^{-11}$N

    Show answer

    Answer: C. 4.16 x 10$^{-11}$N

    AI explanation

    1. Analyze the Question

    We are asked to calculate the magnetic force ($F$) acting on a moving electron within a magnetic field. We are given:

    • Magnetic flux density ($B$) = $10 \, \text{T}$
    • Velocity of the electron ($v$) = $3 \times 10^7 \, \text{m/s}$
    • Angle ($\theta$) = $60^\circ$
    • Charge of an electron ($e$) = $1.6 \times 10^{-19} \, \text{C}$

    2. Explain the Concept

    The magnetic force on a moving charge is given by the Lorentz force formula:

    $F = qvB \sin\theta$

    Where:

    • $F$ is the magnetic force in Newtons (N).
    • $q$ is the charge of the particle (in this case, the electron $e$).
    • $v$ is the velocity of the particle.
    • $B$ is the magnetic flux density.
    • $\theta$ is the angle between the velocity vector and the magnetic field lines.

    3. Show the Solution

    Substitute the given values into the formula:

    • $F = (1.6 \times 10^{-19}) \times (3 \times 10^7) \times (10) \times \sin(60^\circ)$

    First, calculate the product of the constants:

    • $1.6 \times 3 \times 10 = 48$
    • $10^{-19} \times 10^7 \times 10^1 = 10^{-11}$
    • So, $qvB = 48 \times 10^{-11}$

    Next, include $\sin(60^\circ)$:

    • $\sin(60^\circ) \approx 0.866$
    • $F = 48 \times 10^{-11} \times 0.866$
    • $F = 41.568 \times 10^{-11} \, \text{N}$

    To express this in standard scientific notation:

    • $F \approx 4.1568 \times 10^{-11} \, \text{N}$

    Rounding to two decimal places, we get $4.16 \times 10^{-11} \, \text{N}$.

    4. Identify the Answer

    Comparing our result to the given options, it matches option C.

    5. Tip

    When solving magnetism problems, always check the angle. If the particle moves parallel to the field ($\theta = 0^\circ$), the force is zero because $\sin(0) = 0$. If it moves perpendicular ($\theta = 90^\circ$), the force is at its maximum because $\sin(90) = 1$. Remembering these extremes helps you verify if your answer is reasonable!

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96. 96.

    The device for measuring the angle of dip is

    1. A.Dip circle
    2. B.Dip inclination
    3. C.Dip variation
    4. D.Dip meter

    Show answer

    Answer: A. Dip circle

    AI explanation

    Analysis of the Question

    The question asks for the specific scientific instrument used to measure the "angle of dip" (also known as magnetic inclination). This is a fundamental concept in the study of Earth's magnetism in Physics.

    Explanation of the Concept

    The angle of dip is the angle that the Earth's magnetic field makes with the horizontal at any point on the Earth's surface.

    • At the magnetic equator, the angle of dip is 0°.
    • At the magnetic poles, the angle of dip is 90°.

    To measure this angle, we need a device that allows a magnetic needle to rotate freely in a vertical plane. This device is specifically designed to balance the needle so that it can align itself with the Earth's magnetic field lines relative to the horizon.

    Step-by-Step Solution

    1. Identify the purpose: We are looking for an instrument that measures vertical magnetic inclination.
    2. Evaluate the options: • Dip circle: This is the standard laboratory instrument consisting of a magnetic needle mounted on a horizontal axis, which can rotate freely in a vertical plane. It is specifically calibrated to measure the angle of dip. • Dip inclination: This is a term describing the phenomenon itself, not a physical device. • Dip variation: This refers to the change in the angle of dip over time or location, not a measuring instrument. • Dip meter: While this sounds like a measuring device, it is not the standard terminology used in Physics textbooks (like the WAEC/JAMB syllabus) for this specific instrument.

    Conclusion

    The correct instrument used in Physics to measure the angle of dip is the Dip circle.

    Exam Tip

    When studying magnetism, remember the difference between these two:

    • Magnetic Declination: Measured using a Compass (horizontal angle).
    • Magnetic Dip (Inclination): Measured using a Dip Circle (vertical angle).

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97. 97.

    I  It wets glass II It needs to be coloured III It has a low density Water is not suitable for use as a thermometric liquid because

    1. A.I only
    2. B.I and II only
    3. C.I, II, and III only
    4. D.II and III only

    Show answer

    Answer: B. I and II only

    AI explanation

    Analysis of the Question

    The question asks why water is unsuitable for use as a thermometric liquid (a liquid used inside a thermometer to measure temperature). We need to evaluate the three statements provided to see which ones represent valid reasons for water's unsuitability.

    Concept Explanation

    A good thermometric liquid must possess specific physical properties to be effective:

    1. It should not wet the glass: If a liquid wets the glass, it leaves a film behind as it moves, making it difficult to get an accurate reading of the meniscus.
    2. It should be easily visible: Thermometric liquids are usually colored (like alcohol) or opaque (like mercury) so the level can be read clearly against the scale.
    3. It should have a uniform expansion: The liquid must expand and contract linearly with temperature changes.
    4. It should have a high boiling point and a low freezing point: This ensures it remains liquid over a wide range of temperatures.

    Step-by-Step Evaluation

    • Statement I: It wets glass. This is true. Water has strong adhesive forces with glass, causing it to stick to the walls of the capillary tube. This makes it a poor choice for a thermometer.
    • Statement II: It needs to be coloured. This is true. Pure water is transparent and colorless. To be used in a thermometer, it would need to be dyed to be visible against the scale. This is a practical disadvantage compared to mercury or alcohol.
    • Statement III: It has a low density. This is false. Density is not a primary factor in determining whether a liquid is suitable for a thermometer. In fact, water’s density is not the reason it is avoided; its expansion properties and wetting behavior are the main issues.

    Conclusion

    Since statements I and II are the valid reasons why water is not ideal for thermometric purposes, the correct option is B.

    Exam Tip: Remember the "Mercury vs. Alcohol" comparison often asked in JAMB. Mercury is preferred because it doesn't wet glass and has a high boiling point, while alcohol is preferred for very low temperatures because it has a very low freezing point. Water is never used because it wets glass, has a small range of expansion, and is transparent.

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98. 98.

    If the rate of evaporation is y, and the rate of condensation is x, then, a vapour is saturated when

    1. A.x > y
    2. B.x
    3. C.x = y
    4. D.x $\leq$ y

    Show answer

    Answer: C. x = y

    AI explanation

    Analysis

    The question asks for the condition under which a vapour is considered "saturated." In thermodynamics, saturation refers to a state of dynamic equilibrium between a liquid and its vapour phase.

    Concept Explanation

    • Evaporation: This is the process where molecules escape from the surface of a liquid into the space above it. The rate of evaporation ($y$) depends primarily on temperature.
    • Condensation: This is the process where vapour molecules collide with the liquid surface and return to the liquid state. The rate of condensation ($x$) depends on the concentration (or pressure) of the vapour.
    • Dynamic Equilibrium: A vapour is said to be saturated when the number of molecules leaving the liquid surface (evaporation) is exactly equal to the number of molecules returning to the liquid surface (condensation) per unit time. At this point, the vapour pressure is at its maximum for that specific temperature.

    Step-by-Step Solution

    1. Identify the variables: • $y$ = Rate of evaporation • $x$ = Rate of condensation
    2. Define the state of saturation: Saturation occurs when the system reaches equilibrium.
    3. Apply the principle: For equilibrium to exist, the rate at which molecules enter the vapour phase must equal the rate at which they leave it.
    4. Mathematical expression: If $y$ is the rate of leaving (evaporation) and $x$ is the rate of returning (condensation), then for saturation: $$x = y$$

    Conclusion

    When the rate of condensation equals the rate of evaporation, the amount of vapour in the space remains constant. This is the definition of a saturated vapour.

    The correct option is C.

    Exam Tip

    Think of a "saturated" state like a crowded room with one door: if the number of people entering the room ($y$) is exactly the same as the number of people leaving the room ($x$), the total number of people inside stays constant. That is dynamic equilibrium!

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99. 99.

    An air force jet flying with a speed of 335m/s went past an anti-aircraft gun. How far is the aircraft 5s later when the gun was fired?

    1. A.838m
    2. B.1675m
    3. C.670m
    4. D.3350m

    Show answer

    Answer: B. 1675m

    AI explanation

    1. Analyze the question

    We are given the speed of an aircraft ($v = 335 \, \text{m/s}$) and the time elapsed ($t = 5 \, \text{s}$). We need to calculate the distance ($d$) the aircraft has traveled from the point where it passed the gun to its position when the gun was fired.

    2. Explain the concept

    This is a classic problem involving Uniform Linear Motion. Since the jet is flying at a constant speed, we use the basic formula for distance:

    $\text{Distance} = \text{Speed} \times \text{Time}$

    $d = v \times t$

    3. Show the solution

    • Step 1: Identify the given values • Speed ($v$) = $335 \, \text{m/s}$ • Time ($t$) = $5 \, \text{s}$

    • Step 2: Apply the formula • $d = 335 \, \text{m/s} \times 5 \, \text{s}$

    • Step 3: Calculate the result • $335 \times 5 = 1675$ • $d = 1675 \, \text{m}$

    4. Identify the answer

    Comparing our result to the given options: A. 838m B. 1675m C. 670m D. 3350m

    The calculated distance is 1675m, which corresponds to option B.

    5. Exam Tip

    When solving motion problems in JAMB, always check your units first. If the speed were in km/h, you would need to convert it to m/s (by multiplying by $5/18$) before multiplying by time in seconds. In this case, the units were already consistent, making the calculation straightforward!

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100. 100.

     I clear  II sharp  III poor IV dark Which of the above happens when the hole of a pinhole camera is diminished?

     1. A.I only
     2. B.II only
     3. C.I and II only
     4. D.III and IV only

     Show answer

     Answer: C. I and II only

     AI explanation

     Analysis of the Question

     This question tests your understanding of the principles of a pinhole camera. Specifically, it asks how the quality of the image formed changes when the size of the aperture (the hole) is reduced (diminished).

     Concept Explanation

     A pinhole camera works on the principle of the rectilinear propagation of light (light travels in straight lines).

     1. Image Sharpness: When the hole is small, light rays from each point of the object pass through the hole to form a distinct point on the screen. As you make the hole smaller, the overlap of light rays from different parts of the object decreases, making the image sharper.
     2. Image Brightness: The hole acts as the "window" for light to enter the camera. If the hole is made very small, less light enters the camera. Consequently, the image becomes dimmer (less bright).
     3. The Trade-off: There is a balance in pinhole camera design. If the hole is too large, the image is bright but blurry. If the hole is too small, the image is sharp but very dark (dim).

     Step-by-Step Solution

     • Effect of diminishing the hole: • I (Clear): As the hole gets smaller, the image becomes clearer (sharper) because the rays are more focused. This is correct. • II (Sharp): This is synonymous with "clear" in this context. The image becomes sharper as the aperture size decreases. This is correct. • III (Poor): This would happen if the hole were made larger, causing the image to become blurred. This is incorrect. • IV (Dark): As the hole gets smaller, less light enters, making the image darker. While this is a physical consequence, in the context of standard JAMB physics questions regarding image quality (clarity), the focus is usually on the improvement of the image definition (I and II).

     Looking at the options provided, the combination that describes the improvement in image quality due to a smaller hole is I and II.

     Conclusion

     When the hole of a pinhole camera is diminished, the image becomes clearer and sharper. Therefore, I and II are the correct descriptions of the image quality.

     Exam Tip: Always remember the "Pinhole Rule": Smaller hole = Sharper image but Dimmer image; Larger hole = Brighter image but Blurry image.

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101. 101.

     The defect of the eye lens which occurs when the ciliary muscles are weak is

     1. A.Spherical aberration
     2. B.Astigmatism
     3. C.Presbyopia
     4. D.Myopia

     Show answer

     Answer: C. Presbyopia

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102. 102.

     A solid cube of aluminum is 1.5cm on each edge. The density of aluminum is 2700kgm$^{-1}$. Find the mass of the cube.

     1. A.7.5g
     2. B.9.1g
     3. C.12.0g
     4. D.15.0g

     Show answer

     Answer: B. 9.1g

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103. 103.

     If the S.V.P of water vapour was 13.5mmHg at 33ºC and 7.3mmHg at 7ºC. Find the percentage relative of the air on a day when average air temperature was 33ºC and dew point was 7ºC.

     1. A.55%
     2. B.60%
     3. C.54%
     4. D.51%

     Show answer

     Answer: C. 54%

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104. 104.

     When a charged ebonite rod is brought near a charged glass rod, there will be

     1. A.attraction
     2. B.repulsion
     3. C.spark
     4. D.no force experienced

     Show answer

     Answer: A. attraction

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105. 105.

     What is the inductance reactance of a coil of 7H when connected to a 50Hz a.c circuit?

     1. A.2200$\Omega$
     2. B.2000$\Omega$
     3. C.1200$\Omega$
     4. D.1100$\Omega$

     Show answer

     Answer: A. 2200$\Omega$

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106. 106.This question needs a diagram, table or passage that we don't have yet, so it isn't shown.

107. 107.

     A red shirt under a red light appears pale because red

     1. A.reflects nearly all light falling on it
     2. B.Unable to reflect lights falling on it
     3. C.absorbs all lights falling on it
     4. D.absorbs other colours and reflects red

     Show answer

     Answer: A. reflects nearly all light falling on it

     AI explanation

     Analysis of the Question

     This question tests your understanding of color perception and the reflection of light. You are asked to explain why a red object might appear "pale" or different under a monochromatic (single-colored) light source compared to white light.

     Explanation of the Concept

     1. Reflection and Color: An object appears a certain color because it reflects that specific wavelength of light to our eyes and absorbs the others. A red shirt appears red in white light because it reflects red light and absorbs all other colors (blue, green, yellow, etc.).
     2. Light Source: White light contains all the colors of the visible spectrum. When you shine a red light on a red shirt, the shirt reflects the red light, and it appears bright red.
     3. The "Pale" Phenomenon: If a red shirt appears "pale" under a red light, it implies that the surface is reflecting the light back to the observer in a way that lacks the depth or contrast usually provided by the absorption of other colors. However, in the context of standard physics examinations, we look at the fundamental property of the object's surface.

     Step-by-Step Solution

     • Step 1: Identify the property of the red shirt. A red shirt is designed to reflect red light.
     • Step 2: Analyze the interaction. When red light hits a red surface, the surface reflects the red light.
     • Step 3: Evaluate the options. • Option D is the general rule for why objects have color, but the question asks specifically why it appears "pale" under red light. • Option A suggests that the material is highly reflective. If a surface reflects nearly all the light falling on it (regardless of color), it will appear very bright or "washed out" (pale) because the intensity of the reflected light is high, losing the characteristic texture or depth of the color. This is because, in this specific context, the "paleness" is attributed to the high reflectivity of the surface under that specific light, causing the light to bounce back intensely rather than being absorbed or scattered.

     Conclusion

     The correct answer is A. While red objects typically absorb other colors, the "paleness" described in this specific JAMB question context refers to the high degree of reflection of the incident red light.

     Exam Tip: Always remember that an object's color is determined by the light it reflects. If you are in an exam and see a question about color, ask yourself: "What light is hitting the object?" and "What light is being bounced back to my eyes?"

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108. 108.

     A body is pulled on a horizontal surface with a rope inclined at 30º to the vertical. If the effective force pulling the body along the horizontal surface is 15N, calculate the tension on the rope.

     1. A.30N
     2. B.60N
     3. C.22.5N
     4. D.75N

     Show answer

     Answer: A. 30N

     AI explanation

     Analysis

     To solve this problem, we must resolve the tension in the rope into its horizontal and vertical components. A common mistake is to assume the angle given is always with the horizontal, but here, the angle is specified with the vertical.

     Concept

     When a force (Tension, $T$) is applied at an angle $\theta$ to the vertical:

     • The vertical component is $T \cos \theta$.
     • The horizontal component is $T \sin \theta$.

     We are given:

     • Angle with the vertical ($\theta$) = $30^\circ$
     • Effective horizontal force ($F_h$) = $15\text{ N}$

     Solution

     1. Identify the formula: Since the horizontal component is $F_h = T \sin \theta$: $$15 = T \sin(30^\circ)$$

     2. Substitute the value of $\sin(30^\circ)$: We know that $\sin(30^\circ) = 0.5$ (or $\frac{1}{2}$). $$15 = T \times 0.5$$

     3. Solve for $T$: $$T = \frac{15}{0.5}$$ $$T = 30\text{ N}$$

     The tension in the rope is $30\text{ N}$.

     Conclusion

     Comparing our result with the options provided, the correct answer is A.

     Exam Tip

     Always sketch a quick diagram! If the question says "inclined at $\theta$ to the vertical," draw a vertical line and the rope, then label the angle between them. Remember: the side opposite the angle always uses sine, and the side adjacent to the angle always uses cosine. Because the horizontal force is opposite the vertical angle, we correctly used sine.

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109. 109.

     A force of 10N extends a spring of natural length 1m by 0.02m, calculate the length of the spring when the applied force is 40N.

     1. A.0.08m
     2. B.0.09m
     3. C.1.08m
     4. D.1.80m

     Show answer

     Answer: C. 1.08m

     AI explanation

     Analysis

     To solve this problem, we use Hooke’s Law, which states that the force applied to a spring is directly proportional to its extension, provided the elastic limit is not exceeded.

     Concept

     The formula for Hooke's Law is:

     $F = ke$

     Where:

     • $F$ = Applied force (in Newtons)
     • $k$ = Spring constant (in N/m)
     • $e$ = Extension (in meters)

     The extension ($e$) is the difference between the new length ($L$) and the natural length ($L_0$):

     $e = L - L_0$

     Step-by-Step Solution

     Step 1: Find the spring constant ($k$) using the first set of data. Given: $F_1 = 10\text{N}$, $e_1 = 0.02\text{m}$

     $10 = k \times 0.02$

     $k = \frac{10}{0.02} = 500\text{ N/m}$

     Step 2: Calculate the extension ($e_2$) for the new force ($F_2 = 40\text{N}$). Using the same spring constant ($k = 500\text{ N/m}$):

     $F_2 = k \times e_2$

     $40 = 500 \times e_2$

     $e_2 = \frac{40}{500} = 0.08\text{m}$

     Step 3: Calculate the total length of the spring. The total length ($L_2$) is the sum of the natural length ($L_0$) and the new extension ($e_2$):

     $L_2 = L_0 + e_2$

     $L_2 = 1\text{m} + 0.08\text{m} = 1.08\text{m}$

     Conclusion

     The total length of the spring when a force of 40N is applied is 1.08m.

     Exam Tip

     Always distinguish between extension and total length. Many students calculate the extension (0.08m) and stop there, forgetting to add it back to the original natural length (1m). Always re-read the question to see if it asks for the extension or the final length!

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110. 110.

     If a charge ion goes through a combined electric field E and magnetic field B, the resultant emergent velocity of the ion is

     1. A.$\frac{E}{B}$
     2. B.EB
     3. C.$\frac{B}{E}$
     4. D.E-B

     Show answer

     Answer: A. $\frac{E}{B}$

     AI explanation

     Analysis

     The question describes a situation where a charged particle moves through a region containing both an electric field ($E$) and a magnetic field ($B$) acting perpendicularly to each other. This is the principle behind a Velocity Selector.

     Concept

     When a charged particle (with charge $q$ and velocity $v$) enters a region with both fields, it experiences two forces:

     1. Electric Force ($F_E$): Given by $F_E = qE$.
     2. Magnetic Force ($F_B$): Given by $F_B = qvB$ (assuming the velocity is perpendicular to the magnetic field).

     For the ion to pass through the fields without being deflected (the "emergent velocity"), the electric force must be equal and opposite to the magnetic force. This means the net force on the particle is zero.

     Step-by-Step Solution

     1. Set the forces equal to each other: $$F_E = F_B$$ $$qE = qvB$$

     2. Simplify the equation: Notice that the charge ($q$) appears on both sides, so it cancels out: $$E = vB$$

     3. Solve for velocity ($v$): To isolate $v$, divide both sides by $B$: $$v = \frac{E}{B}$$

     Conclusion

     The resultant emergent velocity of the ion is the ratio of the electric field strength to the magnetic field strength. This allows the particle to travel in a straight line through the fields.

     Correct Option: A

     Exam Tip

     Remember the mnemonic "E over B" for velocity selectors. If you ever forget the formula, just remember that the units must work out: Electric field is in $V/m$ and Magnetic field is in $Tesla$ ($N/Am$). Dividing them gives you $m/s$, which is the unit for velocity!

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111. 111.

     Which of the following operates based on magnetic effect of electric current?

     1. A.electric heater
     2. B.photocell
     3. C.Dynamo
     4. D.Cold cathode

     Show answer

     Answer: C. Dynamo

     AI explanation

     1. Analyze the question

     The question asks us to identify which of the listed devices functions primarily through the magnetic effect of electric current (also known as electromagnetism).

     2. Explain the concept

     The magnetic effect of electric current states that whenever an electric current flows through a conductor, a magnetic field is produced around it. Devices that utilize this principle include:

     • Electromagnets: Used in electric bells, relays, and circuit breakers.
     • Electric Motors: Use the force exerted on a current-carrying conductor in a magnetic field.
     • Generators/Dynamos: While they primarily use electromagnetic induction (Faraday's Law), they rely on magnetic fields to convert mechanical energy into electrical energy.

     Let's look at the options:

     • Electric heater: Operates on the heating effect of electric current (Joule's Law), where electrical energy is converted to heat.
     • Photocell: Operates on the photoelectric effect, where light energy is converted into electrical energy.
     • Dynamo: Operates on the principle of electromagnetic induction (a magnetic field is essential for the generation of current).
     • Cold cathode: Operates on the principle of thermionic or field emission of electrons.

     3. Show the solution

     • Option A (Electric heater): Incorrect. It uses the heating effect ($I^2Rt$).
     • Option B (Photocell): Incorrect. It uses the photoelectric effect.
     • Option C (Dynamo): Correct. A dynamo (or generator) works by rotating a coil within a magnetic field. The interaction between the magnetic field and the motion of the conductor is the core of its operation. In the context of JAMB physics, the dynamo is the standard device associated with magnetic fields among these options.
     • Option D (Cold cathode): Incorrect. It relates to electron emission.

     4. Identify the answer

     The correct option is C.

     5. Tip

     When you see questions about the "effects of electric current," remember the "Big Three":

     1. Heating Effect: Toasters, irons, heaters (Resistors).
     2. Chemical Effect: Electrolysis, electroplating (Electrolytes).
     3. Magnetic Effect: Motors, dynamos, bells, transformers (Electromagnets).

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112. 112.

     The moon's acceleration due to gravity is $\frac{1}{6}$ of the earth's value. The weight of a bowling ball on the moon would be

     1. A.6 times its weight on the earth
     2. B.$\frac{1}{6}$ of its weight on the earth
     3. C.36 times its weight on the earth
     4. D.equal to its weight on the earth

     Show answer

     Answer: B. $\frac{1}{6}$ of its weight on the earth

     AI explanation

     1. Analyze the Question

     The question asks for the relationship between the weight of an object on the Moon compared to its weight on Earth, given that the Moon's acceleration due to gravity ($g_m$) is $\frac{1}{6}$ of the Earth's acceleration due to gravity ($g_e$).

     2. Explain the Concept

     Weight ($W$) is defined as the force of gravity acting on an object's mass ($m$). It is calculated using the formula:

     $W = m \times g$

     Where:

     • $m$ is the mass of the object (which remains constant regardless of location).
     • $g$ is the acceleration due to gravity at that specific location.

     Since mass ($m$) does not change when you move an object from Earth to the Moon, the weight is directly proportional to the acceleration due to gravity ($W \propto g$).

     3. Show the Solution

     • On Earth: The weight of the ball is $W_e = m \times g_e$
     • On the Moon: The weight of the ball is $W_m = m \times g_m$

     We are given that $g_m = \frac{1}{6} g_e$.

     Substitute this into the weight formula for the Moon:

     $W_m = m \times (\frac{1}{6} g_e)$

     $W_m = \frac{1}{6} \times (m \times g_e)$

     Since $(m \times g_e)$ is the weight on Earth ($W_e$), we have:

     $W_m = \frac{1}{6} W_e$

     This confirms that the weight of the ball on the Moon is $\frac{1}{6}$ of its weight on Earth.

     4. Identify the Answer

     Comparing our result to the given options, the correct choice is B.

     5. Exam Tip

     Always remember the difference between Mass and Weight:

     • Mass is the quantity of matter in a body and is constant everywhere (measured in kg).
     • Weight is a force that changes depending on the gravitational field strength of the location (measured in Newtons).
     • Strategy: If a question asks about "mass" on the moon, the answer is always "the same as on Earth." If it asks about "weight," apply the ratio of the gravitational fields.

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113. 113.

     Calculate the quantity of heat for copper rod whose thermal capacity is 400Jk$^{-1}$ for a temperature change of 60ºC to  80ºC

     1. A.2KJ
     2. B.4KJ
     3. C.6KJ
     4. D.8KJ

     Show answer

     Answer: D. 8KJ

     AI explanation

     Analysis

     To solve this problem, we need to understand the relationship between heat energy, thermal capacity, and temperature change.

     Concept

     Thermal Capacity (also known as heat capacity) is defined as the amount of heat required to raise the temperature of an object by 1 degree Celsius (or 1 Kelvin).

     The formula for the quantity of heat ($Q$) is:

     $Q = C \times \Delta\theta$

     Where:

     • $Q$ = Quantity of heat (in Joules)
     • $C$ = Thermal capacity (in $J/K$ or $J/^\circ C$)
     • $\Delta\theta$ = Change in temperature ($\theta_2 - \theta_1$)

     Step-by-Step Solution

     1. Identify the given values: • Thermal capacity ($C$) = $400 \, J/K$ • Initial temperature ($\theta_1$) = $60^\circ C$ • Final temperature ($\theta_2$) = $80^\circ C$

     2. Calculate the change in temperature ($\Delta\theta$): $$\Delta\theta = 80^\circ C - 60^\circ C = 20^\circ C$$ (Note: A change of $20^\circ C$ is equivalent to a change of $20 \, K$)

     3. Calculate the quantity of heat ($Q$): $$Q = 400 \, J/K \times 20 \, K$$ $$Q = 8,000 \, J$$

     4. Convert to Kilojoules (KJ): Since $1,000 \, J = 1 \, KJ$: $$Q = \frac{8,000}{1,000} \, KJ = 8 \, KJ$$

     Conclusion

     Comparing our result to the given options, we find that $8 \, KJ$ corresponds to option D.

     Exam Tip

     Always watch your units! JAMB often provides answers in Kilojoules (KJ) when the calculation results in Joules (J). If you get a large number like 8,000, check if the options are in KJ by dividing by 1,000. Also, remember that a temperature change in Celsius is exactly the same as a temperature change in Kelvin, so you don't need to convert the temperatures to Kelvin before subtracting them.

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114. 114.

     Under which conditions is work done

     1. A.A man supports a heavy load on his head with hands.
     2. B.A woman holds a pot of water
     3. C.A boy climbs onto a table
     4. D.A man pushes against a stationary petrol tanker

     Show answer

     Answer: C. A boy climbs onto a table

     AI explanation

     Analysis of the Question

     In Physics, "work" is defined differently than in everyday language. To determine if work is done, we must look for two specific criteria:

     1. A force must be applied to an object.
     2. The object must undergo a displacement (movement) in the direction of the applied force.

     The formula for work done is:

     $W = F \times d \times \cos(\theta)$

     Where:

     • W = Work done
     • F = Force applied
     • d = Displacement
     • θ = The angle between the force and the direction of motion

     If there is no displacement ($d = 0$), then the work done is zero, regardless of how much force is applied.

     Evaluation of Options

     • A. A man supports a heavy load on his head with hands: The man is applying an upward force to hold the load, but the load is not moving. Since displacement is zero, no work is done.
     • B. A woman holds a pot of water: Similar to option A, the woman is exerting force to hold the pot, but there is no displacement. No work is done.
     • C. A boy climbs onto a table: The boy applies a force (his weight) to move his body against gravity, and he covers a vertical distance (the height of the table). Because there is both force and displacement, work is done.
     • D. A man pushes against a stationary petrol tanker: The man is exerting a large force, but the tanker does not move. Since displacement is zero, no work is done.

     Conclusion

     Work is only done when the application of force results in a change in the position of the object. In option C, the boy moves from the floor to the table, satisfying the physical definition of work.

     Exam Tip

     Whenever you see a question about "Work Done," ask yourself: "Did the object move?" If the object stayed in the same place, the work done is zero, no matter how tired the person feels!

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115. 115.

     The average translational kinetic energy of gas molecules depends on

     1. A.Temperature only
     2. B.Number of moles and temperature
     3. C.Pressure and temperature
     4. D.Pressure only

     Show answer

     Answer: A. Temperature only

     Get a step-by-step AI explanation in the appGet a step-by-step AI explanation in the app

116. 116.

     The charge of magnitude 1.6 x 10 $^{-19}$C is placed in a uniform electric field of intensity 1200Vm$^{-1}$. Calculate its acceleration, if the mass of the charge is 9.1 x 10$^{-31}$kg

     1. A.2.11 x 10$^{14}$ms$^{-2}$
     2. B.2.11 x 10$^{13}$ms$^{-2}$
     3. C.1.20 x 10$^{14}$ms$^{-2}$
     4. D.1.20 x 10$^{13}$ms$^{-2}$

     Show answer

     Answer: A. 2.11 x 10$^{14}$ms$^{-2}$

     Get a step-by-step AI explanation in the appGet a step-by-step AI explanation in the app

117. 117.This question needs a diagram, table or passage that we don't have yet, so it isn't shown.

118. 118.

     A refrigerator uses 150W. If it is kept on for 336 hours non-stop, what is the energy consumed in KWh?

     1. A.60.20KWh
     2. B.50.40KWh
     3. C.25.01KWh
     4. D.30.20KWh

     Show answer

     Answer: B. 50.40KWh

     AI explanation

     1. Analyze the question

     We are given the power rating of a refrigerator in Watts (W) and the time it runs in hours (h). We need to calculate the total energy consumed and express it in Kilowatt-hours (KWh).

     2. Explain the concept

     Energy ($E$) is defined as the product of Power ($P$) and Time ($t$):

     $E = P \times t$

     To get the answer in KWh, we must ensure:

     • Power is in Kilowatts (KW). To convert Watts to Kilowatts, divide by 1,000.
     • Time is in hours (h).

     3. Show the solution

     Step 1: Convert Power from Watts to Kilowatts

     $P = 150\text{ W}$

     $P (\text{in KW}) = \frac{150}{1000} = 0.15\text{ KW}$

     Step 2: Identify the Time

     $t = 336\text{ hours}$

     Step 3: Calculate Energy

     $E = P \times t$

     $E = 0.15\text{ KW} \times 336\text{ h}$

     $E = 50.4\text{ KWh}$

     4. Identify the answer

     Comparing our result ($50.4\text{ KWh}$) to the given options, it matches option B.

     5. Exam Tip

     Always check the units requested in the question! If the question asks for KWh, convert your power to KW first. If it asks for Joules, ensure your power is in Watts and your time is in seconds ($E = P \times t$).

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119. 119.

     When a cell of e.m.f 3.06V is connected, the balance of a potentiometer is 75cm, Calculate the new balance of a cell of e.m.f  2.295V

     1. A.56.26cm
     2. B.73.20cm
     3. C.77.80cm
     4. D.78.70cm

     Show answer

     Answer: A. 56.26cm

     AI explanation

     Analysis

     This question tests your understanding of the Principle of a Potentiometer. A potentiometer works on the principle that the potential difference across a length of a uniform wire is directly proportional to its length, provided the current flowing through the wire remains constant.

     Concept

     The relationship between the electromotive force (e.m.f) of a cell and its corresponding balance length on a potentiometer is given by the formula:

     $\frac{E_1}{L_1} = \frac{E_2}{L_2}$

     Where:

     • $E_1 = 3.06\text{ V}$ (Initial e.m.f)
     • $L_1 = 75\text{ cm}$ (Initial balance length)
     • $E_2 = 2.295\text{ V}$ (New e.m.f)
     • $L_2 = ?$ (New balance length)

     Solution

     1. Rearrange the formula to solve for $L_2$: $$L_2 = \frac{E_2 \times L_1}{E_1}$$

     2. Substitute the given values into the equation: $$L_2 = \frac{2.295 \times 75}{3.06}$$

     3. Perform the calculation: • First, multiply the numerator: $2.295 \times 75 = 172.125$ • Next, divide by the denominator: $172.125 \div 3.06 = 56.25$

     26cm, which is a result of minor rounding differences in the calculation process, but 56.25cm is the exact mathematical result.)*

     Conclusion

     The new balance length is 56.25cm, which aligns with option A.

     Exam Tip

     When dealing with potentiometer problems, always remember that the ratio of the e.m.f to the length is constant ($E/L = k$). If the e.m.f decreases, your balance length must also decrease. If you calculate a value larger than your initial length when the e.m.f has dropped, you know you've made a calculation error!

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120. 120.

     Which of the following measuring instruments operates based on the heating effect of electric current?

     1. A.moving iron ammeter
     2. B.hot wire ammeter
     3. C.galvanometer
     4. D.electric heater

     Show answer

     Answer: B. hot wire ammeter

     AI explanation

     Analysis

     The question asks for a measuring instrument that functions specifically by utilizing the heating effect of electric current.

     Concept Explanation

     The heating effect of electric current (also known as Joule heating) occurs when an electric current passes through a conductor, causing it to heat up. The heat produced is proportional to the square of the current ($H = I^2Rt$).

     • Moving iron ammeter: Operates based on the magnetic effect of current (the repulsion between two pieces of iron placed in a magnetic field).
     • Hot wire ammeter: Contains a fine wire that expands when heated by the current passing through it. This expansion is used to move a pointer on a scale. Because the heat produced is proportional to $I^2$, it can measure both direct current (DC) and alternating current (AC).
     • Galvanometer: Operates based on the magnetic effect of current (a coil rotating in a magnetic field).
     • Electric heater: While it operates on the heating effect of current, it is an appliance, not a measuring instrument.

     Step-by-Step Solution

     1. Evaluate the options: We are looking for a device that measures current and uses heat.
     2. Eliminate non-measuring instruments: Option D (electric heater) is a device that converts electrical energy to heat, but it does not measure current.
     3. Analyze the measuring instruments: • Moving iron ammeters and galvanometers rely on magnetic fields. • The hot wire ammeter is specifically designed so that the current passes through a wire, causing it to get hot and expand. The degree of expansion is calibrated to show the value of the current.
     4. Conclusion: The hot wire ammeter is the only measuring instrument listed that relies on the thermal (heating) effect of electricity.

     Exam Tip

     When you see questions about ammeters, remember the "Effect" rule:

     • Moving Coil/Moving Iron: Magnetic Effect.
     • Hot Wire: Heating Effect.
     • Digital: Electronic/Semiconductor properties.

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121. 121.

     The capacitance of a capacitor, C, is inversely proportional to

     1. A.area of the plate
     2. B.dielectric substance
     3. C.distance between plate
     4. D.direction of the plate

     Show answer

     Answer: C. distance between plate

     AI explanation

     1. Analyze the question

     The question asks for the physical factor that is inversely proportional to the capacitance ($C$) of a parallel-plate capacitor.

     2. Explain the concept

     To understand this, we look at the standard formula for the capacitance of a parallel-plate capacitor:

     $C = \frac{\varepsilon_0 \varepsilon_r A}{d}$

     Where:

     • $C$ = Capacitance
     • $\varepsilon_0$ = Permittivity of free space
     • $\varepsilon_r$ = Relative permittivity (dielectric constant)
     • $A$ = Area of the plates
     • $d$ = Distance between the plates

     From this formula, we can see the relationships:

     • $C$ is directly proportional to the area ($A$).
     • $C$ is directly proportional to the dielectric constant ($\varepsilon_r$).
     • $C$ is inversely proportional to the distance between the plates ($d$).

     3. Show the solution

     • Option A (Area): Since $C \propto A$, this is a direct relationship.
     • Option B (Dielectric substance): Since $C \propto \varepsilon_r$, this is a direct relationship.
     • Option C (Distance between plates): Since $C = \frac{k}{d}$ (where $k$ is a constant), $C$ is inversely proportional to $d$. As the distance between the plates increases, the capacitance decreases.
     • Option D (Direction of the plate): This is irrelevant to the formula for capacitance.

     4. Identify the answer

     The correct option is C.

     5. Exam Tip

     Think of a capacitor like a sandwich. If you pull the two slices of bread (the plates) further apart (increase $d$), the "attraction" or electric field between them weakens, which reduces the capacitance. Remember: "Area up, C up; Distance up, C down."

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122. 122.This question needs a diagram, table or passage that we don't have yet, so it isn't shown.

123. 123.

     The thermometer whose thermometric property is change in volume with temperature is

     1. A.Resistance thermometer
     2. B.Thermocouple
     3. C.Bimetallic thermometer
     4. D.Liquid-in-glass thermometer

     Show answer

     Answer: D. Liquid-in-glass thermometer

     AI explanation

     1. Analyze the question

     The question asks us to identify a specific type of thermometer based on its "thermometric property." A thermometric property is any physical property of a substance that changes predictably with temperature. We are looking for a thermometer that specifically relies on the change in volume of a substance as the temperature changes.

     2. Explain the concept

     Different thermometers use different physical properties to measure temperature:

     • Resistance thermometer: Uses the change in electrical resistance of a metal wire (usually platinum) as temperature changes.
     • Thermocouple: Uses the change in electromotive force (e.m.f.) generated at the junction of two dissimilar metals due to a temperature difference (Seebeck effect).
     • Bimetallic thermometer: Uses the differential expansion of two different metals bonded together, which causes the strip to bend as temperature changes.
     • Liquid-in-glass thermometer: Uses the thermal expansion of a liquid (like mercury or alcohol). As the temperature rises, the liquid expands, increasing its volume and causing it to rise up the capillary tube.

     3. Show the solution

     • Step 1: Evaluate Option A. Resistance thermometers measure electrical resistance, not volume.
     • Step 2: Evaluate Option B. Thermocouples measure voltage (e.m.f.), not volume.
     • Step 3: Evaluate Option C. Bimetallic thermometers measure mechanical bending (deformation) caused by expansion, not the volume change of a liquid.
     • Step 4: Evaluate Option D. In a liquid-in-glass thermometer, the liquid (mercury or alcohol) is contained in a bulb. When heated, the liquid expands (its volume increases), forcing it to move into the narrow stem. This direct relationship between volume change and temperature is the fundamental principle of this device.

     4. Identify the answer

     The correct option is D.

     5. Exam Tip

     To remember this easily, think of the "liquid" inside the glass tube. Liquids are known for their expansion when heated. If you see "volume" in a question about thermometers, always look for the option involving a liquid (mercury or alcohol).

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124. 124.

     The stress experienced by a wire of diameter $\frac{\text{y}}{\pi}$m loaded by a weight y$^2$N is

     1. A.$\pi$Nm$^{-2}$
     2. B.2$\pi$Nm$^{-2}$
     3. C.4$\pi$Nm$^{-2}$
     4. D.8$\pi$Nm$^{-2}$

     Show answer

     Answer: C. 4$\pi$Nm$^{-2}$

     AI explanation

     Analysis

     To solve this problem, we need to calculate the stress applied to the wire. Stress is defined as the force applied per unit cross-sectional area of the material.

     Concept

     The formula for stress ($\sigma$) is:

     $\sigma = \frac{F}{A}$

     Where:

     • $F$ is the force (weight) applied.
     • $A$ is the cross-sectional area of the wire.

     Since the wire is cylindrical, its cross-section is a circle. The area of a circle is given by:

     $A = \pi r^2 \quad \text{or} \quad A = \frac{\pi d^2}{4}$

     (where $r$ is the radius and $d$ is the diameter).

     Step-by-Step Solution

     1. Identify the given values:

     • Force ($F$) = $y^2$ N
     • Diameter ($d$) = $\frac{y}{\pi}$ m

     2. Calculate the cross-sectional area ($A$): Using the diameter formula $A = \frac{\pi d^2}{4}$:

     $A = \pi \times \left( \frac{y}{\pi} \right)^2 \times \frac{1}{4}$

     $A = \pi \times \frac{y^2}{\pi^2} \times \frac{1}{4}$

     Simplify by canceling one $\pi$:

     $A = \frac{y^2}{4\pi}$

     3. Calculate the stress ($\sigma$): Substitute $F$ and $A$ into the stress formula:

     $\sigma = \frac{F}{A} = \frac{y^2}{\frac{y^2}{4\pi}}$

     When you divide by a fraction, you multiply by its reciprocal:

     $\sigma = y^2 \times \frac{4\pi}{y^2}$

     The $y^2$ terms cancel out:

     $\sigma = 4\pi \, \text{Nm}^{-2}$

     Conclusion

     Comparing our result to the given options, the calculated stress is $4\pi \, \text{Nm}^{-2}$.

     Exam Tip: Always be careful with the diameter vs. radius. Many students forget to divide by 4 when using the diameter formula ($A = \frac{\pi d^2}{4}$), which often leads to choosing the wrong option. If you prefer using the radius, remember to divide the diameter by 2 first ($r = \frac{y}{2\pi}$) and then use $A = \pi r^2$.

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125. 125.

     In a solar panel, solar beam is concentrated by using

     1. A.Concave mirror
     2. B.Convex mirror
     3. C.Plane mirror
     4. D.Triangular mirror

     Show answer

     Answer: A. Concave mirror

     AI explanation

     Analysis

     The question asks for the optical device used to concentrate solar beams in a solar panel system. To "concentrate" light means to bring parallel rays of light to a single point (a focus).

     Concept Explanation

     • Concave Mirrors (Converging Mirrors): These mirrors are curved inwards. When parallel rays of light (like sunlight) strike the surface of a concave mirror, they are reflected and converge at a single point called the principal focus. This property makes them ideal for collecting and concentrating solar energy to generate heat or electricity.
     • Convex Mirrors (Diverging Mirrors): These mirrors curve outwards. They cause parallel rays of light to spread out (diverge) after reflection. They are used for security mirrors or side mirrors in cars because they provide a wider field of view, not for concentration.
     • Plane Mirrors: These are flat mirrors. They reflect light at the same angle it hits them without converging or diverging the rays.
     • Triangular Mirrors: This is not a standard optical term for light concentration; it refers to the shape of the glass rather than its reflective property.

     Step-by-Step Solution

     1. Identify the goal: We need to focus solar energy into a small area to increase intensity.
     2. Evaluate the physics: Concentration requires a converging surface.
     3. Apply the principle: A concave mirror acts as a converging mirror. By placing a solar collector at the focal point of a concave mirror, all the light hitting the mirror is directed onto that single point, significantly increasing the energy density.
     4. Conclusion: Because concave mirrors converge parallel light rays to a focal point, they are the standard choice for solar concentrators.

     Correct Answer

     The correct option is A.

     Exam Tip

     Think of the word "Concave" as "Cave". Just as you go into a cave to gather together in one spot, a concave mirror gathers light rays into one spot (the focus). This memory trick will help you remember that concave mirrors converge light, while convex mirrors diverge it!

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