DeeepSolve Logo
DeeepSolve
Get app
WAEC (WASSCE) 2021

2021 WAEC (WASSCE) Physics Past Questions and Answers

The 2021 WAEC (WASSCE) Physics past questions with answers: 50 objective questions from the 2021 paper in the DeeepSolve question bank, each with its answer behind "Show answer". Try each question before you check, then practise the paper as a timed WAEC-style CBT.

Past questions © the examination body (JAMB/WAEC/NECO). DeeepSolve is not affiliated with them. Rights holders: see /copyright.

Questions

  1. 1.

    The handle of a screw jack is 35 cm long and the pitch of the screw is 0.5 cm. What force must be applied at the end of the handle to lift a load of 2000N, if the efficiency of the jack is 30% [π = 227\frac{22}{7}]?

    1. A.152.0N
    2. B.132.0N
    3. C.15.2N
    4. D.440.0N
    Show answer

    Answer: C. 15.2N

    AI explanation

    Analyze the question: A screw jack has a handle (effort arm) of radius r = 35 cm and a screw pitch of 0.5 cm. We need the effort F that lifts a load of 2000 N when the efficiency is 30%.

    Concept:

    • Velocity ratio of a screw jack: VR = 2πr / pitch
    • Mechanical advantage: MA = Load / Effort
    • Efficiency = MA / VR × 100%

    Solution:

    1. Velocity ratio: VR = 2πr / p = (2 × 22/7 × 35) / 0.5 = 220 / 0.5 = 440
    1. Use the efficiency: Efficiency = (MA / VR) × 100 30 = (MA / 440) × 100 MA = 0.30 × 440 = 132
    1. Find the effort: MA = Load / Effort Effort = 2000 / 132 ≈ 15.15 N ≈ 15.2 N

    Checking the options: 132 is the mechanical advantage, not the force, so B is a trap. The effort is about 15.2 N, which matches option C.

    Answer: C (15.2 N)

    Tip: For screw jack questions, always compute VR = 2πr/pitch first, then MA = efficiency × VR, then Effort = Load/MA. Don't stop at MA, because a number like 132 appears as a distractor option.

    AI can make mistakes. Report anything that looks wrong.

  2. 2.

    The distance between a node and its adjacent antinode of a transverse wave is equal to?

    1. A.half of the wavelength.
    2. B.the wavelength.
    3. C.thrice the wavelength.
    4. D.quarter of the wavelength.
    Show answer

    Answer: D. quarter of the wavelength.

    AI explanation

    Step 1: Analyze the question We need the distance between a node and the antinode right next to it in a stationary (standing) wave.

    Step 2: Concept In a stationary wave:

    • A node is a point of zero displacement.
    • An antinode is a point of maximum displacement.
    • The distance between two adjacent nodes is λ/2.
    • The distance between two adjacent antinodes is also λ/2.
    • Between two adjacent nodes there is exactly one antinode, right in the middle.

    Step 3: Solution Distance from node to adjacent node = λ/2. The antinode lies halfway between them, so:

    Node to adjacent antinode = ½ × (λ/2) = λ/4

    Step 4: Answer The distance is a quarter of the wavelength, which is option D.

    Tip: Remember the sequence along a standing wave: Node → (λ/4) → Antinode → (λ/4) → Node. So N to N = λ/2, and N to adjacent A = λ/4. Don't confuse "node to node" (half wavelength) with "node to antinode" (quarter wavelength), as WAEC loves testing this.

    AI can make mistakes. Report anything that looks wrong.

  3. 3.

    Which of the following statements is an effect of compressing gas molecules at constant temperature?

    1. A.The pressure on the molecules decreases.
    2. B.The molecules gain more kinetic energy.
    3. C.The molecules make more impact per second on the walls of the container.
    4. D.The molecules increase in size.
    Show answer

    Answer: C. The molecules make more impact per second on the walls of the container.

    AI explanation

    Analyze the question: A gas is compressed (its volume is reduced) while its temperature stays constant. We need the effect on the molecules.

    Concept: Boyle's law and the kinetic theory of gases.

    • At constant temperature, PV = constant. If volume decreases, pressure increases.
    • Temperature is a measure of the average kinetic energy of the molecules. If temperature is constant, the average kinetic energy does not change.
    • Molecules do not change in size when a gas is compressed. Only the spaces between them shrink.

    Solution, checking each option:

    • A. The pressure decreases. Wrong. By Boyle's law, reducing the volume increases the pressure.
    • B. The molecules gain more kinetic energy. Wrong. The temperature is constant, so the average kinetic energy stays the same.
    • C. The molecules make more impact per second on the walls of the container. Correct. In a smaller volume, the molecules have a shorter distance to travel between collisions with the walls. The collision frequency rises, so the force per unit area (pressure) rises.
    • D. The molecules increase in size. Wrong. Molecular size does not change with compression.

    **Answer: C.

    Tip: For "constant temperature" gas questions, remember that the speed and kinetic energy of the molecules stay the same. The only change is the collision rate, which is why the pressure goes up. Think "squeeze, so more hits, so more pressure."

    AI can make mistakes. Report anything that looks wrong.

  4. 4.

    Opening in the eye through which light passes to the retina is called the?

    1. A.pupil
    2. B.cornea.
    3. C.iris
    4. D.optic nerve.
    Show answer

    Answer: A. pupil

    AI explanation

    Step 1: Analyze the question The question asks for the opening in the eye through which light passes to reach the retina. The key word is "opening", meaning a hole or gap, not a tissue or a nerve.

    Step 2: Explain the concept (parts of the eye)

    • Cornea: the transparent front covering of the eye. It does most of the bending (refraction) of light, but it is a covering, not an opening.
    • Iris: the coloured muscular ring. It controls how much light enters by changing the size of the opening, but it is not the opening itself.
    • Pupil: the circular opening at the centre of the iris. Light passes through it to the lens and then to the retina.
    • Optic nerve: carries electrical signals from the retina to the brain. Light does not pass through it.

    Step 3: Work through the options

    • A. Pupil: it is the opening in the iris, so it fits.
    • B. Cornea: a transparent layer, not an opening. Wrong.
    • C. Iris: it surrounds the opening and controls its size. Wrong.
    • D. Optic nerve: it transmits signals, not light. Wrong.

    Step 4: Answer The correct option is A. pupil.

    Tip: Remember that the iris is the "door-keeper" and the pupil is the "door". In bright light the iris makes the pupil smaller, and in dim light it makes the pupil larger. The cornea is like the "window glass" at the front of the eye.

    AI can make mistakes. Report anything that looks wrong.

  5. 5.

    Which of the following factors is not among that determines the resistance of a wire?

    1. A.mass
    2. B.cross-sectional area
    3. C.length
    4. D.material
    Show answer

    Answer: A. mass

    AI explanation

    Analyze the question: We need the factor that does not determine the resistance of a wire.

    Concept: The resistance of a uniform wire is given by

    R = ρL / A

    where:

    • ρ = resistivity, which depends on the material (and temperature)
    • L = length of the wire
    • A = cross-sectional area

    So resistance increases with length, decreases with a larger cross-sectional area, and depends on the material. Temperature also affects it.

    Checking each option:

    • A. Mass: Mass does not appear in the formula. It is not a direct determining factor. Two wires of different mass can have the same resistance if their ρ, L and A are the same. Mass is related to the wire's volume and density, but it is not an independent factor in resistance.
    • B. Cross-sectional area: Appears in the formula, so it is a factor.
    • C. Length: Appears in the formula, so it is a factor.
    • D. Material: Determines resistivity ρ, so it is a factor.

    Answer: The factor that is not among those determining resistance is mass, which is option A.

    Tip: Remember "R = ρL/A". Anything not in this formula (such as mass, colour, or shape of coiling) is not a direct factor. The usual factors to list are length, cross-sectional area, material, and temperature.

    AI can make mistakes. Report anything that looks wrong.

  6. 6.

    A heat sensitive resistor made of a semiconductor is called?

    1. A.thermometer.
    2. B.thermostat.
    3. C.thermistor
    4. D.thermopile.
    Show answer

    Answer: C. thermistor

    AI explanation

    Step 1: Analyze the question The question asks for the name of a device that is (a) a resistor, (b) made of a semiconductor, and (c) sensitive to heat (temperature).

    Step 2: Explain the concept The word comes from combining two words:

    • Thermo = heat/temperature
    • Resistor = a component that opposes current flow

    So a thermistor ("thermal resistor") is a semiconductor device whose resistance changes noticeably with temperature. There are two types:

    • NTC (Negative Temperature Coefficient): resistance decreases as temperature rises (the most common).
    • PTC (Positive Temperature Coefficient): resistance increases as temperature rises.

    Step 3: Check each option

    • A. Thermometer: a general instrument for measuring temperature. It is not specifically a semiconductor resistor.
    • B. Thermostat: a switch-based device that keeps temperature constant, as in irons, refrigerators and water heaters.
    • C. Thermistor: a heat-sensitive semiconductor resistor. This matches the description.
    • D. Thermopile: a number of thermocouples connected in series, used to detect or measure radiant heat. It is not a resistor.

    Step 4: Answer The correct option is C. thermistor.

    Exam tip: Break the word apart. "Thermo" + "(res)istor" = thermistor. In the same way, a photoresistor (LDR) is a light-sensitive resistor. Also remember that a thermostat stats (keeps constant) the temperature, while a thermopile is a pile (stack) of thermocouples.

    AI can make mistakes. Report anything that looks wrong.

  7. 7.

    A man weighing 200 N runs up a staircase in 5s. If the height of the staircase is 9 m, calculate the power of the man.

    1. A.1000 W
    2. B.360 W
    3. C.40 W
    4. D.1800 W
    Show answer

    Answer: B. 360 W

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

  8. 8.

    Which of the following factors does not affect the rate of evaporation of a liquid?

    1. A.temperature
    2. B.volume
    3. C.wind
    4. D.surface area
    Show answer

    Answer: B. volume

    AI explanation

    Analyze the question: We need the factor that does NOT affect how fast a liquid evaporates.

    Concept: Evaporation happens at the surface of a liquid, when the faster-moving molecules escape into the air. The rate depends on:

    1. Temperature: Higher temperature gives molecules more kinetic energy, so more escape. This affects the rate.
    2. Surface area: A larger exposed surface lets more molecules escape at once. This affects the rate.
    3. Wind (air movement): Wind carries away vapour molecules above the surface, so fewer return to the liquid. This affects the rate.
    4. Humidity: If the air is already moist, evaporation is slower.
    5. Nature of the liquid: Volatile liquids like ethanol or petrol evaporate faster than water.

    Check each option:

    • A. Temperature: affects the rate.
    • B. Volume: the amount of liquid does not change how quickly molecules leave the surface. A cup of water and a bucket of water with the same surface area and conditions evaporate at the same rate per unit area. The larger volume simply takes longer to dry up completely. So volume does not affect the rate.
    • C. Wind: affects the rate.
    • D. Surface area: affects the rate.

    Answer: B. Volume.

    Tip: Evaporation is a surface phenomenon. If a factor is not about the surface, the molecules' energy, or the air above the surface, it probably doesn't affect the rate. Remember "TASH": Temperature, Area, Surrounding air movement (wind), Humidity.

    AI can make mistakes. Report anything that looks wrong.

  9. 9.

    Which of the sketched graphs above illustrates the correct variation of the gravitational force, Fg between two objects and the distance, d, between the centre

    1. A.A
    2. B.B
    3. C.C
    4. D.D
    Show answer

    Answer: C. C

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

  10. 10.

    A note produced by an instrument is distinguished from a similar note produced by another instrument by the?

    1. A.intensity,
    2. B.pitch.
    3. C.overtones.
    4. D.loudness
    Show answer

    Answer: C. overtones.

    AI explanation

    Analyze the question: Two instruments (say a piano and a guitar) can play the same note, with the same pitch and the same loudness. Yet we can still tell them apart. The question asks which property makes this possible.

    Concept: characteristics of sound

    • Intensity/loudness: related to the amplitude of the vibration, so how strong or soft a sound is.
    • Pitch: related to frequency, so how high or low a note is.
    • Quality (timbre): the characteristic that distinguishes notes of the same pitch and loudness from different instruments. It depends on the number and relative strengths of the overtones (harmonics) present in the note.

    Step-by-step solution:

    1. Two instruments playing the same note have the same fundamental frequency, so the pitch is the same. This eliminates B.
    2. Both can be played at the same loudness/intensity, so A and D cannot be what tells them apart.
    3. What differs is the mix of overtones that each instrument produces along with the fundamental. This gives each instrument its own quality or timbre.
    4. So the note from one instrument is distinguished from a similar note from another by its overtones.

    Answer: C. overtones

    Exam tip: Remember the trio: pitch → frequency, loudness → amplitude, quality (timbre) → overtones. If a question says "same note, different instruments," the answer is nearly always quality, which is linked to overtones or harmonics.

    AI can make mistakes. Report anything that looks wrong.

  11. 11.

    Which of the following statements about distance and displacement is not correct?

    1. A.Displacement is a vector quantity.
    2. B.Distance has dimension
    3. C.Displacement is measured in meters.
    4. D.Distance is a vector quantity.
    Show answer

    Answer: D. Distance is a vector quantity.

    AI explanation

    Step 1: Analyze the question We are asked to find the statement that is not correct about distance and displacement. So three options are true and one is false.

    Step 2: Key concepts

    • Distance is the total length of the path travelled. It is a scalar quantity (magnitude only, no direction).
    • Displacement is the shortest straight-line distance from the starting point to the end point, in a specified direction. It is a vector quantity (magnitude and direction).
    • Both are lengths, so both have the dimension L and are measured in metres (m) in SI units.

    Step 3: Check each option

    • A. Displacement is a vector quantity. Correct, because it has both magnitude and direction.
    • B. Distance has dimension. Correct. Distance has the dimension of length, [L].
    • C. Displacement is measured in meters. Correct. The SI unit of displacement is the metre.
    • D. Distance is a vector quantity. Incorrect. Distance is a scalar, since it has magnitude only.

    Step 4: Answer The statement that is not correct is D.

    Exam tip: Remember "Distance = Directionless" (scalar), while "Displacement = Direction included" (vector). When a question says "not correct", look for the false statement, not the true one. Many students lose marks by misreading this.

    AI can make mistakes. Report anything that looks wrong.

  12. 12.

    The reason for laminating the soft iron core of a  transformer is to?

    1. A.reduce eddy current.
    2. B.reduce magnetic flux.
    3. C.increase the magnetic flux.
    4. D.reduce its efficiency.
    Show answer

    Answer: A. reduce eddy current.

    AI explanation

    1. Analyze the question The question asks why the soft iron core of a transformer is made of thin laminated sheets instead of one solid block.

    2. Explain the concept When the alternating current in the primary coil creates a changing magnetic flux, that flux also induces unwanted circulating currents inside the iron core itself. These are called eddy currents. They cause:

    • Heating of the core (energy wasted as heat)
    • Reduced efficiency of the transformer

    3. Show the solution

    • A solid iron core offers a large cross-sectional area, so large eddy currents can circulate.
    • If the core is built from many thin sheets (laminations) that are insulated from each other with varnish or oxide layers, the eddy current paths are broken up.
    • Smaller paths mean higher resistance to the eddy currents, so they become much weaker.
    • Less eddy current means less heat loss and higher efficiency.

    Checking the options:

    • A. Reduce eddy current: Correct, this is exactly the purpose of lamination.
    • B. Reduce magnetic flux: Wrong. The core is there to carry the flux, not to reduce it.
    • C. Increase magnetic flux: Wrong. Flux linkage is provided by the soft iron's high permeability, not by lamination.
    • D. Reduce its efficiency: Wrong. Lamination improves efficiency.

    4. Answer The correct option is A. reduce eddy current.

    5. Tip Remember the pairing: Laminated core → less eddy current → less heat loss. Other ways to reduce transformer losses that often appear in exams:

    • Soft iron core reduces hysteresis loss.
    • Thick copper wire reduces copper (resistive) loss.
    • Laminated core reduces eddy current loss.

    AI can make mistakes. Report anything that looks wrong.

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

  14. 14.

    A wire of cross-sectional area 2π  x  10−8^-{8} m2^2 and resistivity 1.1 x 10−8^-{8} Ω m, has a resistance of 21Ω. Calculate the length of the wire. [π=22/7]

    1. A.180 m
    2. B.140 m
    3. C.120 m
    4. D.240 m
    Show answer

    Answer: C. 120 m

    AI explanation

    Concept: The resistance of a wire is given by R = ρL/A, so L = RA/ρ.

    Given:

    • R = 21 Ω
    • A = 2π × 10⁻⁸ m², with π = 22/7
    • ρ = 1.1 × 10⁻⁸ Ω m

    Step 1: Find A A = 2 × (22/7) × 10⁻⁸ = (44/7) × 10⁻⁸ m²

    Step 2: Substitute into L = RA/ρ L = (21 × (44/7) × 10⁻⁸) / (1.1 × 10⁻⁸)

    The 10⁻⁸ terms cancel: L = (21 × 44/7) / 1.1 L = (3 × 44) / 1.1 L = 132 / 1.1 L = 120 m

    Answer: C (120 m)

    Tip: Simplify before multiplying. Here 21/7 = 3 made the arithmetic easy, and the powers of 10 cancelled. Always rearrange the formula first (L = RA/ρ) and cancel the common factors.

    AI can make mistakes. Report anything that looks wrong.

  15. 15.

    A current of 2A passes through a wire of resistance 4Ω for 3 minutes. Calculate the energy lost.

    1. A.960J
    2. B.1440J
    3. C.2880J
    4. D.48J
    Show answer

    Answer: C. 2880J

    AI explanation

    Analyze the question: A current flows through a resistor for a given time. The electrical energy converted to heat (energy lost) is required.

    Concept: Energy dissipated in a resistor is given by Joule's law:

    W = I²Rt

    where I is current (A), R is resistance (Ω), and t is time in seconds.

    Solution:

    • I = 2 A
    • R = 4 Ω
    • t = 3 minutes = 3 × 60 = 180 s

    W = I²Rt W = (2)² × 4 × 180 W = 4 × 4 × 180 W = 16 × 180 W = 2880 J

    Answer: The energy lost is 2880 J, which matches option C.

    Tip: The most common mistake is forgetting to convert minutes to seconds. If you used t = 3, you would get 48 J (option D), which is a trap. Always convert time to seconds before using joule-based formulas. Also remember the three forms of the heat formula: W = I²Rt = VIt = V²t/R.

    AI can make mistakes. Report anything that looks wrong.

  16. 16.

    An atom that emits an a-particle?

    1. A.may become a different element.
    2. B.becomes a different isotope of the element.
    3. C.daughter with increased mass.
    4. D.becomes a daughter of a different element always.
    Show answer

    Answer: D. becomes a daughter of a different element always.

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

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

  18. 18.

    Which of the arrangements of radiations below shows decreasing order of wavelengths?

    1. A.X-rays> radio waves > infrared radiations
    2. B.Radio waves> infrared radiations > X-rays
    3. C.Infrared radiations > radio waves > X-rays
    4. D.X-rays> infrared radiations > radio waves
    Show answer

    Answer: B. Radio waves> infrared radiations > X-rays

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

  19. 19.

    A ball is swung in a horizontal circle of centre O with a constant speed. What is the direction of its acceleration?

    1. A.Away from O
    2. B.Along the Circumference of the circle
    3. C.Toward centre O
    4. D.Along a tangent to the circle
    Show answer

    Answer: C. Toward centre O

    AI explanation

    Step 1: Analyze the question A ball moves in a horizontal circle with constant speed. We need the direction of its acceleration.

    Step 2: The concept Acceleration is the rate of change of velocity, and velocity has both magnitude (speed) and direction. Even when the speed is constant, the ball's direction keeps changing as it moves around the circle. So the velocity is changing, which means the ball is accelerating.

    • The velocity always points along the tangent to the circle.
    • The change in velocity (Δv) over a short time points toward the centre.
    • This acceleration is called centripetal acceleration, and its magnitude is:

    a = v²/r = ω²r

    where v is the speed, r is the radius, and ω is the angular velocity.

    Step 3: Why the other options fail

    • A (Away from O): This is the direction of the "centrifugal" effect, which is not a real force acting on the ball. The real net force is inward.
    • B (Along the circumference): The circumference is curved, and the direction of motion at any instant is along the tangent, not toward some point along the arc.
    • D (Along a tangent): This is the direction of the velocity, not the acceleration. If there were tangential acceleration, the speed would be changing, but here the speed is constant, so the tangential component is zero.

    Step 4: Answer The acceleration is directed toward the centre O.

    Exam tip: Remember "Velocity is tangent, acceleration is centre." For uniform circular motion, the force and acceleration always point toward the centre (centripetal means "centre-seeking"). If you see "constant speed in a circle," think of an inward acceleration straight away.

    AI can make mistakes. Report anything that looks wrong.

  20. 20.

    Which of the following statements about the molecules of solids and liquids is correct? They both

    1. A.have weak attraction.
    2. B.have wide separations.
    3. C.exhibit random motion.
    4. D.exhibit vibratory motion.
    Show answer

    Answer: D. exhibit vibratory motion.

    AI explanation

    Analyze the question: We need the one property that is true of the molecules of both solids and liquids.

    Concept: Under the kinetic theory of matter:

    | Property | Solids | Liquids | Gases | |---|---|---|---| | Intermolecular attraction | Very strong | Moderate | Very weak | | Separation | Very close | Close | Far apart | | Motion | Vibrate about fixed positions | Vibrate, and also move/slide past one another | Random, rapid, free motion |

    Checking each option:

    • A. Weak attraction: Wrong. Solids have strong forces, and liquids have moderately strong forces. Weak attraction is typical of gases.
    • B. Wide separations: Wrong. Molecules in both solids and liquids are closely packed. Wide separations belong to gases.
    • C. Random motion: Wrong for solids. Solid molecules are held in fixed positions and cannot move randomly through the substance. Random translational motion is typical of gases (and, to a degree, liquids).
    • D. Vibratory motion: Correct. Solid molecules vibrate about fixed positions. Liquid molecules also vibrate (as well as moving past each other), so both exhibit vibratory motion.

    Answer: D.

    Tip: Remember the pattern for motion: solids vibrate, liquids vibrate and flow, gases move randomly. When a question asks what solids and liquids have in common, look for "close together" or "vibration". Words like "weak" and "wide" or "random" usually point to gases.

    AI can make mistakes. Report anything that looks wrong.

  21. 21.

    An electric circuit consists of a resistor. a battery and a key. If the voltage of the battery is increased, there Would be an increase in the?

    1. A.current and resistance only.
    2. B.current resistance and temperature.
    3. C.current and temperature only.
    4. D.resistance and temperature only
    Show answer

    Answer: B. current resistance and temperature.

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

  22. 22.

    A student wishes to measure the potential difference across a resistor,R. She has a galvanometer,G and some connecting wires. What else does she need?

    1. A.high value resistor connected in parallel with G
    2. B.. low value resistor connected in parallel with G low value
    3. C.resistor connected in series with G
    4. D.high value resistor connected in series with G.
    Show answer

    Answer: D. high value resistor connected in series with G.

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

  23. 23.

    The electrons in a cathode-ray tube are produced by?

    1. A.heating a metal filament.
    2. B.ionization of the air.
    3. C.applying a magnetic field to the y-plates.
    4. D.applying an electric field to the x-plates.
    Show answer

    Answer: A. heating a metal filament.

    AI explanation

    Analyze the question: It asks how a cathode-ray tube (CRT) produces its electrons, meaning the source of the electrons, not how they are deflected or focused.

    Concept: Thermionic emission In a CRT, the electron gun contains a cathode with a heated filament. When a metal is heated strongly, some of its free electrons gain enough energy to overcome the metal's surface binding energy (the work function) and escape. This process is called thermionic emission. A high positive potential at the anode then accelerates these electrons into a beam.

    Checking each option:

    • A. Heating a metal filament. Correct. This is thermionic emission, the actual source of electrons in a CRT.
    • B. Ionization of the air. Wrong. A CRT is a highly evacuated tube, so there is almost no air. Ionizing gas is how a gas discharge tube works, not a CRT.
    • C. Applying a magnetic field to the y-plates. Wrong. The Y-plates are electric deflection plates that move the beam vertically. They do not produce electrons.
    • D. Applying an electric field to the x-plates. Wrong. The X-plates deflect the beam horizontally. They only steer electrons that already exist.

    Summary of CRT parts:

    1. Heated filament and cathode: produce electrons.
    2. Grid: controls the brightness (the number of electrons).
    3. Anodes: accelerate and focus the beam.
    4. X- and Y-plates: deflect the beam.
    5. Fluorescent screen: glows where electrons strike it.

    Answer: A. Electrons in a CRT are produced by heating a metal filament (thermionic emission).

    Exam tip: Remember "Produce = Heat, Steer = Plates". If a question asks where electrons come from, think of heating (thermionic emission). If it asks about deflection, think of the X- and Y-plates.

    AI can make mistakes. Report anything that looks wrong.

  24. 24.

    Determine the speed of the wave.

    1. A.64 cm/s
    2. B.32 cm/s
    3. C.24 cm/s
    4. D.72 cm/s
    Show answer

    Answer: C. 24 cm/s

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

  25. 25.

    Formation of hydrogen bubbles at the copper plate of a primary cell is called?

    1. A.polarization.
    2. B.back e.m.f.
    3. C.electrolysis.
    4. D.local action.
    Show answer

    Answer: A. polarization.

    AI explanation

    Analyze the question: It asks for the name of the defect in a simple (voltaic) cell where hydrogen bubbles collect on the copper plate (the positive electrode).

    Explain the concept: In a simple cell, zinc and copper plates are placed in dilute sulphuric acid.

    • Zinc reacts with the acid and releases electrons.
    • Hydrogen ions (H⁺) from the acid move to the copper plate, pick up electrons and form hydrogen gas.
    • The hydrogen gas forms a layer of bubbles on the copper plate.

    This layer causes two problems:

    1. It insulates the copper plate from the electrolyte, which increases the internal resistance of the cell.
    2. It sets up a reverse potential, so the current falls quickly.

    This defect is called polarization. It is cured by adding a depolarizer such as manganese(IV) oxide (MnO₂), which oxidizes the hydrogen to water. This is what happens in the Leclanché cell.

    Check the other options:

    • B. Back e.m.f.: This is an opposing e.m.f. in a circuit, for example in motors or electrolysis cells. It is not the name for hydrogen bubbles forming on a plate.
    • C. Electrolysis: This is the chemical decomposition of a substance by passing an electric current through it. It is not the defect described here.
    • D. Local action: This is the defect caused by impurities in the zinc, which form tiny cells and make the zinc waste away. It is cured by amalgamating the zinc with mercury.

    Answer: The formation of hydrogen bubbles at the copper plate is polarization, which is option A.

    Exam tip: Remember these two pairs:

    • Polarization → hydrogen bubbles on the copper → cured by a depolarizer (MnO₂).
    • Local action → impurities in the zinc → cured by amalgamation (mercury).

    AI can make mistakes. Report anything that looks wrong.

  26. 26.

    The components of vectors Q and R are (-3.0, 5.5) and (9.2, 4.4) respectively. Determine the components of Q + R.

    1. A.(3.7, 7.4)
    2. B.(6.2, 9.9)
    3. C.(2.5, -4 .8).
    4. D.(14.7, 1.4)
    Show answer

    Answer: B. (6.2, 9.9)

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

  27. 27.

    An electric pressing iron is connected to the mains using an insulated wire. wire becomes very hot. The heat generated in the wire can be minimized by replacing the wire with one of?

    1. A.thinner insulation.
    2. B.greater diameter.
    3. C.smaller diameter.
    4. D.thicker insulation.
    Show answer

    Answer: B. greater diameter.

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

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

  29. 29.

    Which of the following statements is not a characteristic of a plane progressive wave?

    1. A.Energy travels out through the medium
    2. B.Neighboring points along the profile possess different amplitudes
    3. C.Neighboring points along the profile possess the same amplitude
    4. D.Neighboring particles vibrate with different phase
    Show answer

    Answer: B. Neighboring points along the profile possess different amplitudes

    AI explanation

    Analyze the question: We need the statement that is NOT a characteristic of a plane progressive wave.

    Concept: A plane progressive (travelling) wave carries energy through a medium from one point to another. Its key features are:

    • Energy is transported in the direction of travel (A is true).
    • Every particle vibrates with the same amplitude, because no energy is lost in an ideal wave (C is true).
    • Each particle vibrates with the same frequency and period, but at a different phase from its neighbours. The disturbance reaches each point at a slightly different time, so the phase changes along the wave (D is true).

    Checking each option:

    • A. Energy travels out through the medium. This is true, so it is not the answer.
    • B. Neighbouring points have different amplitudes. This is false. In a progressive wave all particles have the same amplitude. (Different amplitudes along the medium is a feature of stationary waves, where nodes have zero amplitude and antinodes have maximum amplitude.)
    • C. Neighbouring points have the same amplitude. This is true.
    • D. Neighbouring particles vibrate with different phase. This is true.

    Answer: B is the statement that is NOT a characteristic of a plane progressive wave.

    Tip: Remember the contrast:

    • Progressive wave: same amplitude everywhere, phase varies, energy is transported.
    • Stationary wave: amplitude varies (nodes and antinodes), no net energy transport.

    When a question says "not a characteristic", test each option against the true properties and pick the one that fails.

    AI can make mistakes. Report anything that looks wrong.

  30. 30.

    Which of the following set of quantities have members which are all vectors?

    1. A.Pressure, energy and force
    2. B.Force, displacement and momentum
    3. C.Distance, acceleration and work
    4. D.Density, volume and weight
    Show answer

    Answer: B. Force, displacement and momentum

    AI explanation

    Analyze the question: We need the option in which every quantity has both magnitude and direction (vectors).

    Concept:

    • Vector: has magnitude and direction (e.g. force, displacement, velocity, acceleration, momentum, weight).
    • Scalar: has magnitude only (e.g. distance, speed, mass, energy, work, pressure, density, volume).

    Checking each option:

    • A. Pressure, energy and force: Pressure is a scalar and energy is a scalar. Only force is a vector. ✗
    • B. Force, displacement and momentum: Force is a vector (it acts in a direction). Displacement is a vector (distance in a specified direction). Momentum (mass × velocity) is a vector, with the direction of the velocity. All three are vectors. ✓
    • C. Distance, acceleration and work: Distance is a scalar and work is a scalar. Only acceleration is a vector. ✗
    • D. Density, volume and weight: Density and volume are scalars. Only weight is a vector. ✗

    Answer: Option B is the only set in which every member is a vector.

    Tip: Ask yourself, "Do I need to say which way?" If yes, it is a vector. Remember that work, energy, pressure, distance, speed, mass, density and volume are scalars. Do not be confused by pressure: it acts on surfaces, but it is still a scalar. Also, work is force × displacement, but it is a scalar because it comes from a dot product.

    AI can make mistakes. Report anything that looks wrong.

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

  32. 32.

    Electric motor primarily converts?

    1. A.electrical energy to chemical energy.
    2. B.kinetic energy to potential energy
    3. C.electrical energy to mechanical energy
    4. D.electrical energy to heat energy.
    Show answer

    Answer: C. electrical energy to mechanical energy

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

  33. 33.

    A radioactive material has a half-life of 1.0 hour If 200.0 g of it was present at 6 a.m. on a certain day, how many grams will have decayed by 9 a.m. on the same day?

    1. A.175.0 g
    2. B.150.0 g
    3. C.100.0 g
    4. D.187.5 g
    Show answer

    Answer: A. 175.0 g

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

  34. 34.

    A rotating disc contains a set of holes in a circle. An air jet is directed onto the holes and a note of frequency 480 Hz is produced. If the number of holes is 20, calculate the speed of rotation of the disc.

    1. A.10 rev/s
    2. B.20 rev/s
    3. C.24 rev/s
    4. D.8 rev/s.
    Show answer

    Answer: C. 24 rev/s

    AI explanation

    Analyze the question: This is a siren. As the disc rotates, each hole lets a puff of air through. The frequency of the note is the number of puffs per second. Concept: Frequency of note = (number of holes) × (rotations per second) f = n × N where f = 480 Hz, n = 20 holes, and N = rotation speed in rev/s. Solution: N = f / n N = 480 / 20 N = 24 rev/s Tip: For siren questions, remember that each hole gives one pulse per revolution, so frequency = holes × revolutions per second. If the question asks for a different quantity, just rearrange the formula. Always check that your units are rev/s and not rev/min.

    AI can make mistakes. Report anything that looks wrong.

  35. 35.

    Which of the following statements about the universal gravitational constant, G, is true?

    1. A.It is fundamental quantity.
    2. B.It has dimension  M-¹L³T-².
    3. C.Its S.I. unit is N m2^2kg
    4. D.It is a vector quantity
    Show answer

    Answer: B. It has dimension  M-¹L³T-².

    AI explanation

    Analyze the question: We need to find the true statement about the universal gravitational constant, G.

    Concept: Newton's law of gravitation says F = GMm/r², so

    G = Fr²/(Mm)

    Step-by-step solution:

    1. Dimension of force: F = MLT⁻²
    2. Dimension of r²: L²
    3. Dimension of Mm: M²

    G = (MLT⁻² × L²) / M² = M⁻¹L³T⁻²

    Checking each option:

    • A. Fundamental quantity: False. Fundamental (base) quantities are mass, length, time, and so on. G is a derived constant, and its dimension is built from M, L and T.
    • B. Dimension M⁻¹L³T⁻²: True, as shown above.
    • C. S.I. unit N m² kg: False. The correct unit is N m² kg⁻², not N m² kg. The kg should be in the denominator and squared.
    • D. Vector quantity: False. G is a scalar constant with magnitude only (6.67 × 10⁻¹¹ N m² kg⁻²).

    Tip: For dimension questions, rearrange the formula to make the required constant the subject, then substitute the dimensions of each term. Also remember that the unit of G is N m² kg⁻², which is the same as m³ kg⁻¹ s⁻².

    AI can make mistakes. Report anything that looks wrong.

  36. 36.

    Which of the following quantities is not an example of force?

    1. A.Mass
    2. B.Tension
    3. C.Weight
    4. D.Friction
    Show answer

    Answer: A. Mass

    AI explanation

    Analyze the question: We need the one quantity that is not a force.

    Concept: A force is a push or a pull that can change the shape, speed, or direction of a body. It is a vector quantity measured in newtons (N). Mass, on the other hand, is the amount of matter in a body. It is a scalar quantity measured in kilograms (kg).

    Check each option:

    • A. Mass: This is the quantity of matter in an object, measured in kg. It is not a push or a pull, so it is not a force.
    • B. Tension: This is the pulling force transmitted along a string, rope, or cable. It is a force.
    • C. Weight: This is the gravitational force acting on a body, W = mg. It is measured in newtons, so it is a force.
    • D. Friction: This is the force that opposes relative motion between two surfaces in contact. It is a force.

    Answer: Mass is the only quantity here that is not a force.

    Tip: Students often confuse mass and weight. Remember that mass is measured in kg and stays the same everywhere, while weight is measured in N and changes with gravity (W = mg). If the unit is the newton, it is a force.

    AI can make mistakes. Report anything that looks wrong.

  37. 37.

    Which of the following units is equivalent to the unit of electric current?

    1. A.C s−1{-1}
    2. B.W
    3. C.J s−1{-1}
    4. D.C
    Show answer

    Answer: A. C s−1{-1}

    AI explanation

    Analyze the question: We need the unit that is equivalent to the ampere (A), the unit of electric current.

    Concept: Current is the rate of flow of charge:

    I = Q / t

    So 1 ampere = 1 coulomb per second, which is 1 C s⁻¹.

    Check each option:

    • A. C s⁻¹ is charge divided by time, which is exactly the definition of current. ✔
    • B. W (watt) is the unit of power, not current. ✘
    • C. J s⁻¹ is energy per time, which is also power (1 W = 1 J s⁻¹). ✘
    • D. C (coulomb) is the unit of charge. ✘

    (The option is written as "C s−1{-1}", which is a formatting glitch for C s⁻¹.)

    Tip: Think "I = Q/t". Any unit written as coulombs per second is amperes. Also remember that J s⁻¹ and W are the same thing (power), so if two options are equivalent to each other, as B and C are here, neither can be the answer to a single-answer question about current.

    AI can make mistakes. Report anything that looks wrong.

  38. 38.

    Which of the following actions will increase capacitance of a parallel plate capacitor? I. Decreasing the distance between the plates II. Increasing the distance between the plates. III. Increasing the area of the plates overlap. IV. Avoiding the use of dielectric between the plate

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

    Answer: A. I and III only

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

  39. 39.

    The acceleration of a moving object can be determined from the?

    1. A.slope of its distance-time graph.
    2. B.area under its distance-time graph.
    3. C.slope of its velocity-time graph.
    4. D.area under its velocity-time graph
    Show answer

    Answer: C. slope of its velocity-time graph.

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

  40. 40.

    Which of the following curved surfaces will produce a real image? I. Concave mirror II. Convex mirror III. Diverging lens IV. Converging lens

    1. A.I and III only
    2. B.I, II and IV only
    3. C.II, III and V only
    4. D.I and IV only
    Show answer

    Answer: D. I and IV only

    AI explanation

    Analyze the question: You are asked which of the four devices can form a real image. A real image is one where light rays actually meet (converge) at a point, so the image can be projected onto a screen.

    Concept:

    • Concave mirror is a converging mirror. When the object is beyond the focal length, it forms a real, inverted image. (When the object is inside the focal length, the image is virtual.)
    • Convex mirror is a diverging mirror. It always forms a virtual, erect, diminished image.
    • Diverging (concave) lens spreads light out. It always forms a virtual, erect, diminished image.
    • Converging (convex) lens converges light. When the object is beyond the focal length, it forms a real, inverted image. This is how a projector or a camera works.

    Solution:

    • I. Concave mirror: can produce a real image ✔
    • II. Convex mirror: virtual only ✘
    • III. Diverging lens: virtual only ✘
    • IV. Converging lens: can produce a real image ✔

    So the devices that can produce a real image are I and IV only.

    Checking the options:

    • A (I and III): III is wrong.
    • B (I, II and IV): II is wrong.
    • C (II, III and V): there is no item V, and II and III are wrong.
    • D (I and IV only): correct ✔

    Tip: Remember that "converging" devices (concave mirror, convex lens) can form real images, while "diverging" devices (convex mirror, concave lens) only form virtual images. A quick way to remember it: only converging devices make real images.

    AI can make mistakes. Report anything that looks wrong.

  41. 41.

    The following statements about a loudspeaker are correct except?

    1. A.its contains a permanent magnet.
    2. B.sound signal converted  to varying current signal enters the speech coil.
    3. C.the current in the speech coil creates a magnetic force on the coil.
    4. D.the magnetic force on the speech coil is uni-directional.
    Show answer

    Answer: D. the magnetic force on the speech coil is uni-directional.

    AI explanation

    Analyze the question: We need the statement about a loudspeaker that is NOT correct (the "except").

    Concept: A moving-coil loudspeaker converts electrical signals into sound using the motor effect (a current-carrying conductor in a magnetic field experiences a force, given by F = BIL).

    How it works:

    1. A permanent magnet provides a steady radial magnetic field.
    2. A sound signal (from a microphone or amplifier) is converted into an alternating, varying electrical current.
    3. This current flows through the speech (voice) coil, which sits in the magnet's field.
    4. The coil experiences a magnetic force, F = BIL.
    5. Because the current alternates in direction, the force alternates too: the coil moves forward, then backward.
    6. The coil is attached to a paper cone (diaphragm), so the cone vibrates and produces sound waves.

    Check each option:

    • A. Correct. A permanent magnet is present.
    • B. Correct. The varying current signal enters the speech coil.
    • C. Correct. The current in the coil in the magnet's field produces a magnetic force on the coil.
    • D. Incorrect. The force is not uni-directional. Since the current alternates, the force reverses direction continually, making the coil and cone vibrate back and forth. If the force were in only one direction, the cone would just be pushed out and stay there, producing no sound waves.

    Tip: For "loudspeaker" questions, remember "varying current → varying force → vibration → sound." A loudspeaker needs a force that changes direction. Also, don't confuse it with a DC motor, which uses a commutator to keep the rotation in one direction.

    AI can make mistakes. Report anything that looks wrong.

  42. 42.

    The inductive reactance in a circuit of frequency 100Hz is 1ohms. Calculate the inductance of the inductor[π = 3.14]

    1. A.2.00 x 10−3_{-3}H
    2. B.1.59 x 10−3_{-3}H
    3. C.1.09 x 10−3_{-3}H
    4. D.6.28x 10−3_{-3}H
    Show answer

    Answer: B. 1.59 x 10−3_{-3}H

    AI explanation

    Analyze the question: We are given the inductive reactance X_L = 1 Ω and frequency f = 100 Hz. We need to find the inductance L. Concept: Inductive reactance is the opposition an inductor offers to alternating current: X_L = 2πfL so L = X_L / (2πf) Solution: L = 1 / (2 × 3.14 × 100) L = 1 / 628 L = 0.001592 H L ≈ 1.59 × 10⁻³ H The options are written with "10₋₃", which is a formatting slip for 10⁻³. Answer: Option B (1.59 × 10⁻³ H) Tip: When you see "reactance" with a frequency, rearrange the formula first, then divide. For inductors, L = X_L / (2πf). For capacitors, C = 1 / (2πfX_C). Remember that 2π ≈ 6.28, so 1/6.28 ≈ 0.159. Spotting that "159" pattern lets you pick the answer quickly in the exam hall. Option D (6.28 × 10⁻³) is the trap for students who multiply by 2π instead of dividing.

    AI can make mistakes. Report anything that looks wrong.

  43. 43.

    A metallic sphere is heated from 27°C to 200°C Without change of state. Which of the following  changes would have resulted from the heating?

    1. A.No changes occur in its volume and density
    2. B.Its volume increases and its density increases
    3. C.Its volume increases and its density decrease
    4. D.Its volume increases without a change in density
    Show answer

    Answer: C. Its volume increases and its density decrease

    AI explanation

    Step 1: Analyze the question A metal sphere is heated from 27°C to 200°C and stays solid. We need to find what happens to its volume and density.

    Step 2: The concept Most solids undergo thermal expansion when heated. The atoms vibrate more strongly and move slightly farther apart, so the volume increases.

    The volume expansion formula is:

    ΔV = V₀ γ Δθ

    where γ is the coefficient of volume expansivity and Δθ is the temperature change.

    Density is given by:

    ρ = mass / volume

    Step 3: Apply it

    • Temperature rises by Δθ = 200 − 27 = 173°C, so the volume increases.
    • The mass stays the same, because no matter is added or removed.
    • Since ρ = m/V, a larger V with a constant m gives a smaller density.

    Step 4: Check the options

    • A. Wrong, because the volume does change.
    • B. Wrong, because the density cannot increase when the volume increases and the mass is constant.
    • C. Correct: the volume increases and the density decreases.
    • D. Wrong, because if the volume changes, the density must change too.

    Step 5: Exam tip Remember: "Heat it up, volume goes up, density goes down" (mass stays the same). In WASSCE and JAMB questions on expansion, always ask yourself whether the mass changes. If it does not, density moves in the opposite direction to volume.

    AI can make mistakes. Report anything that looks wrong.

  44. 44.

    According to Pascal's principle, the pressure in a fluid is always?

    1. A.dependent on density of the fluid.
    2. B.distributed partially in all directions.
    3. C.transmitted equally in all directions.
    4. D.increasing with height.
    Show answer

    Answer: C. transmitted equally in all directions.

    AI explanation

    Step 1: Analyze the question The question asks what Pascal's principle says about pressure in a fluid.

    Step 2: The concept Pascal's principle states that pressure applied to an enclosed fluid is transmitted equally and undiminished to every part of the fluid and to the walls of the container, in all directions.

    This is the principle behind hydraulic brakes, hydraulic jacks, and car lifts (common in Nigerian mechanic workshops). A small force on a small piston creates a pressure P = F/A. That same pressure acts on a larger piston, giving a larger force.

    Step 3: Evaluate each option

    • A. Dependent on density of the fluid. This is true for pressure due to a fluid column (P = ρgh), but it is not Pascal's principle.
    • B. Distributed partially in all directions. Wrong. The pressure is transmitted fully, not partially.
    • C. Transmitted equally in all directions. Correct. This is the direct statement of Pascal's principle.
    • D. Increasing with height. Wrong. Pressure in a fluid increases with depth, not height, and this is a separate idea (P = ρgh).

    Step 4: Answer

    Tip: Link Pascal with "Pressure passes on equally." For Pascal, think "transmitted equally." For P = ρgh, think "depth and density."

    AI can make mistakes. Report anything that looks wrong.

  45. 45.

    A stone is thrown horizontally with initial velocity 15m/s from a tower 20 m high. How long does it take to reach the ground? [g= 10m/s2^2

    1. A.2s
    2. B.4s
    3. C.5s
    4. D.1s
    Show answer

    Answer: A. 2s

    AI explanation

    Analyze the question

    A stone is thrown horizontally from a height of 20 m. We need the time to hit the ground. The horizontal speed (15 m/s) doesn't affect the fall time, because horizontal and vertical motions are independent.

    Concept

    Vertically, the stone starts with zero velocity (it was thrown horizontally) and accelerates downward under gravity:

    h = ut + ½gt², where u = 0 (vertical)

    So h = ½gt², which gives t = √(2h/g)

    Solution

    • h = 20 m
    • g = 10 m/s²

    t = √(2 × 20 / 10) t = √4 t = 2 s

    Check: the vertical distance fallen in 2 s is ½ × 10 × 2² = 20 m ✓

    Answer: The stone takes 2 seconds, so the correct option is A.

    Tip: In projectile questions where an object is launched horizontally, ignore the horizontal speed when finding the time of flight. Use only the vertical formula t = √(2h/g). The 15 m/s would only be needed if the question asked for the horizontal range (R = 15 × 2 = 30 m). Many WASSCE questions include extra data like this to test whether you know which information to use.

    AI can make mistakes. Report anything that looks wrong.

  46. 46.

    Which of the following statements best describes the particles in a solid at room temperature? They are

    1. A.far apart and moving randomly.
    2. B.close together and vibrating.
    3. C.close together and stationary.
    4. D.close together and moving randomly.
    Show answer

    Answer: B. close together and vibrating.

    AI explanation

    Analyze the question: It asks about the arrangement and motion of particles in a solid at room temperature. This comes from the kinetic theory of matter.

    Concept: In a solid, the particles are held in fixed positions by strong intermolecular forces. They are packed closely together in a regular pattern. They cannot move from place to place, but they have kinetic energy, so each particle vibrates about its fixed position. Particles are never completely stationary except at absolute zero (0 K).

    Solution, option by option:

    • A. Far apart and moving randomly: This describes a gas, so it is wrong.
    • B. Close together and vibrating: Solid particles are tightly packed and vibrate about fixed positions, so this is correct.
    • C. Close together and stationary: Particles at room temperature (about 25 °C, far above absolute zero) always have kinetic energy, so they are never stationary. This is wrong.
    • D. Close together and moving randomly: This describes a liquid, where particles slide past each other. It is wrong.

    **Answer: B.

    Exam tip: Remember the three states of matter like this:

    • Solid: close together and vibrating in place
    • Liquid: close together and sliding past each other
    • Gas: far apart and moving rapidly and randomly

    Whenever you see "stationary" in a question about particles, be suspicious. Particles only stop moving at absolute zero.

    AI can make mistakes. Report anything that looks wrong.

  47. 47.

    An ice cube has mass of 20 g at 5°C. Calculate the energy required to raise its temperature to 0°C. [Specific heat capacity of ice = 2.1 J/g°c]

    1. A.105 J
    2. B.100 J
    3. C.42 J
    4. D.210 J
    Show answer

    Answer: D. 210 J

    AI explanation

    Analyze the question: We need the heat energy needed to warm ice from one temperature to another. The ice is only being warmed, not melted, so we use the specific heat capacity formula.

    Concept: Q = mcΔθ

    where m is the mass, c is the specific heat capacity, and Δθ is the change in temperature.

    Solution:

    The question says the ice is at "5°C" and is raised to 0°C. Ice at +5°C isn't physically possible, since it would have melted. This is almost certainly a typo for -5°C, which is the usual form of this question. The temperature change is then:

    Δθ = 0 − (−5) = 5°C

    Substituting:

    • m = 20 g
    • c = 2.1 J/g°C
    • Δθ = 5°C

    Q = 20 × 2.1 × 5 Q = 42 × 5 Q = 210 J

    Check against the options: 210 J matches option D.

    Note on the typo: If you take the numbers literally (5°C to 0°C), the change is still 5 degrees in size, so the magnitude is the same, 210 J (the sign would just be negative, meaning heat is lost).

    Tip: Watch for common slips. Option C (42 J) is what you get if you forget to multiply by the temperature change (20 × 2.1). Option A (105 J) comes from halving the answer by mistake. Always multiply all three quantities: m × c × Δθ.

    Also remember that a change of phase (ice to water at 0°C) would need latent heat, Q = ml, but that isn't needed here because the question stops at 0°C.

    AI can make mistakes. Report anything that looks wrong.

  48. 48.

    Which of the following scientist suggested that moving particles exhibit wave properties?

    1. A.Isaac Newton
    2. B.Ernest Rutherford
    3. C.Louis de Broglie
    4. D.J.J. Thompson
    Show answer

    Answer: C. Louis de Broglie

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

  49. 49.

    A force of 10 N, acting continuously, increases the kinetic energy of an object from 20.J to 60 J. Find the distance moved by the object.

    1. A.200m
    2. B.40m
    3. C.4m
    4. D.400m
    Show answer

    Answer: C. 4m

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

  50. 50.

    If the relative humidity of the atmosphere increases, the rate of evaporation of sweat from the human body?

    1. A.decreases
    2. B.remains the same
    3. C.increases then decreases
    4. D.increases
    Show answer

    Answer: A. decreases

    AI explanation

    Step 1: Analyze the question We're asked what happens to the rate of evaporation of sweat when the relative humidity of the air increases.

    Step 2: Explain the concept Relative humidity (RH) compares the amount of water vapour in the air with the maximum it can hold at that temperature.

    • High RH means the air is already close to saturation, so it can take up very little extra water vapour.
    • Low RH means the air is dry and can absorb a lot more water vapour.

    Evaporation happens when water molecules leave the liquid surface. At the same time, vapour molecules in the air return to the liquid (condensation). If the air already has lots of vapour, more molecules return, so the net rate of evaporation falls.

    Step 3: Apply it to sweat

    • When RH rises, the air near the skin holds more water vapour.
    • Sweat evaporates more slowly, so it stays on the skin.
    • That's why we feel sticky and uncomfortable on humid days (e.g. in Lagos or Port Harcourt during the rainy season), and why cooling by sweating is less effective.
    • On dry, harmattan days (low RH), sweat evaporates quickly and we feel cooler.

    Step 4: Choose the answer Increased relative humidity → decreased rate of evaporation.

    decreases**.

    Tip: Remember "High humidity, slow evaporation." Factors that increase evaporation rate are: higher temperature, larger surface area, wind or air movement, and lower humidity. Humidity works in the opposite direction to the others.

    AI can make mistakes. Report anything that looks wrong.

Frequently asked questions