PHYSICS SAMPLE QUESTIONS ON UNITS AND MEASUREMENTS

 Here are sample WAEC/NECO-style Physics questions on “Units and Measurements”, drawn from the style and difficulty of the last five years’ exams — including both objective (multiple-choice) and theory types, with answers and explanations.

🔹 A. Objective Questions (Multiple Choice)
(Each question carries one mark.)

1. The S.I. unit of electric charge is
A. Volt  B. Ampere  C. Coulomb  D. Ohm
✅ Answer: C. Coulomb
Explanation: ; charge = current × time → A·s = C.

2. Which of the following quantities is dimensionless?
A. Angle  B. Density  C. Pressure  D. Momentum
✅ Answer: A. Angle
Explanation: Angle = arc length / radius → ratio of two lengths → no dimension.

3. Which of the following is a derived quantity?
A. Length  B. Mass  C. Time  D. Force
✅ Answer: D. Force
Explanation: Derived from base quantities → .

4. Which of the following has the same dimension as energy?
A. Power × time  B. Pressure × volume  C. Force × distance  D. All of the above
✅ Answer: D. All of the above
Explanation: Each reduces to , same as Joule.

5. Which of the following pairs correctly represent scalar quantities?
A. Force and Momentum
B. Speed and Distance
C. Displacement and Acceleration
D. Velocity and Force
✅ Answer: B. Speed and Distance

6. Which of the following sets contains only base quantities?
A. Mass, Velocity, Time  B. Length, Mass, Time  C. Volume, Area, Time  D. Force, Pressure, Density
✅ Answer: B. Length, Mass, Time

7. The instrument used to measure the diameter of a thin wire is:
A. Meter rule
B. Vernier caliper
C. Micrometer screw gauge
D. Compass
✅ Answer: C. Micrometer screw gauge

8. The vernier caliper reads 2.4 cm main scale and 0.08 cm vernier scale. What is the total reading?
A. 2.48 cm  B. 2.32 cm  C. 2.08 cm  D. 2.40 cm
✅ Answer: A. 2.48 cm
Explanation: Add main scale + vernier scale reading.

9. The least count of a micrometer screw gauge is
A. 0.1 mm  B. 0.01 mm  C. 0.001 mm  D. 1 mm
✅ Answer: B. 0.01 mm

10. A student measured a length four times and got 10.2 cm, 10.3 cm, 10.3 cm, and 10.4 cm. The average and estimated error are
A. 10.3 ± 0.1 cm  B. 10.3 ± 0.05 cm  C. 10.2 ± 0.2 cm  D. 10.25 ± 0.15 cm
✅ Answer: B. 10.3 ± 0.05 cm
Explanation: Mean = 10.3 cm; error = half range = (10.4 − 10.2)/2 = 0.1 cm → ± 0.05 cm.

11. Which of the following represents a derived unit?
A. Ampere
B. Candela
C. Newton
D. Kelvin
✅ Answer: C. Newton. Newton = kgm/s², a derived unit of force.

12. The physical quantity having the unit kg·m⁻¹·s⁻² is:
A. Pressure
B. Force
C. Work
D. Power
✅ Answer: A. Pressure
Pressure = Force/Area = (kg·m/s²)/m²

13. Which of the following represents a derived unit?
A. Ampere
B. Candela
C. Newton
D. Kelvin
✅ Answer: C. Newton
Newton = kg·m/s², a derived unit of force.

🔹 B. Theory / Structured Questions

1. (a) Define:
(i) Base quantity (ii) Derived quantity.
(b) State any four base quantities and their S.I. units.
✅ Answer Outline:
Base quantity → cannot be defined in terms of others (e.g., mass, length, time, temperature).
Derived quantity → obtained from base quantities (e.g., area = length²).
Examples:
Mass (kg), Length (m), Time (s), Electric current (A), Thermodynamic temperature (K), Luminous intensity (cd), Amount of substance (mol).

2. Explain the difference between accuracy and precision in measurement.
✅ Answer Outline:
Accuracy → closeness to the true value.
Precision → degree of repeatability or consistency in repeated measurements.

3. A student measured the diameter of a steel ball as 1.20 cm, 1.22 cm, 1.21 cm.
Calculate the mean diameter and the percentage error if the instrument’s least count is 0.01 cm.
✅ Solution:
Mean = (1.20 + 1.22 + 1.21)/3 = 1.21 cm
Error = ±0.01 cm
Percentage error = (0.01 / 1.21) × 100 = 0.83%

4. The density of a material is 2.5 g/cm³. Convert it to kg/m³.
✅ Solution:

5. A rectangular block has measured dimensions:
Length = 5.00 cm ± 0.01 cm
Breadth = 3.00 cm ± 0.01 cm
Height = 2.00 cm ± 0.01 cm
Find:
(a) Volume, (b) Percentage error in the volume.
✅ Solution:
Volume .
Fractional error = sum of fractional errors of dimensions.
% error = 0.83%.

6. (a) Define the term dimension of a physical quantity.
(b) Determine the dimensions of:
(i) Energy
(ii) Pressure
(iii) Power
✅ Solution:
Energy = Work = Force × distance = (MLT⁻²) × L = M¹L²T⁻²
Pressure = Force/Area = M¹L⁻¹T⁻²
Power = Energy/time = M¹L²T⁻³

7. State four base quantities and their units.
✅ Answer:
i. Length – metre (m)
ii. Mass – kilogram (kg)
III. Time – second (s)
iv. Electric current – ampere (A)