Which of these is a derived unit?

1. Analyze the question

The question asks you to identify a "derived unit" from the given list. To answer this, we must distinguish between base units (fundamental units) and derived units in the International System of Units (SI).

2. Explain the concept

• Base Units: These are the fundamental units of measurement that do not depend on any other physical quantities. There are seven base units in the SI system, including: • Length (Metre, m) • Mass (Kilogram, kg) • Time (Second, s) • Electric Current (Ampere, A) • Temperature (Kelvin, K) • Amount of substance (Mole, mol) • Luminous intensity (Candela, cd)
• Derived Units: These are units created by combining base units through multiplication or division to express other physical quantities (like speed, force, or pressure). For example, Force is measured in Newtons, which is derived from mass and acceleration ($F = ma$), giving it the base unit equivalent of $kg \cdot m/s^2$.

3. Show the solution

Let's evaluate each option:

• A. Kilogram: This is the SI base unit for mass.
• B. Metre: This is the SI base unit for length.
• C. Newton: This is the unit of force. Since Force = Mass × Acceleration ($kg \times m/s^2$), the Newton is a derived unit because it is composed of base units.
• D. Second: This is the SI base unit for time.

4. Identify the answer

Since the Newton is the only unit on the list formed by combining base units, it is the correct answer.

5. Tip

A quick way to remember this for your JAMB exam is the "Big Seven" rule: If you can memorize the seven base units (Mass, Length, Time, Current, Temperature, Amount, Intensity), any other unit you encounter in Physics (like Joule, Watt, Pascal, or Newton) is almost certainly a derived unit!