A physical quantity is measured as 12.345 ± 0.005 units. The relative error in this measurement is approximately: MCQ with Answer and Explanation

A physical quantity is measured as 12.345 ± 0.005 units. The relative error in this measurement is approximately:
A. 4%
B. 0.004%
C. 0.04%
D. 0.4%
Answer: Option C
Solution (By JKSSB Mock Tests)
Relative error = (Absolute error) / (Measured value) = 0.005 / 12.345 ≈ 0.000405. Converting to percentage: 0.000405 × 100% ≈ 0.0405% ≈ 0.04%. Relative error quantifies precision independent of measurement scale. Absolute error (±0.005) indicates instrument precision. This concept is vital for comparing measurement reliability across different magnitudes. Memory tip: Percentage error = (Absolute error / True value) × 100. Competitive exams often test this calculation with varying significant figures to assess numerical proficiency.

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Practice More Physics Questions

Question #1
The speed of sound in air at 0°C is approximately 332 m/s. At 27°C, it will be approximately:
A. 332 m/s
B. 350 m/s
C. 360 m/s
D. 340 m/s

Correct Answer: Option B


Explanation:
Speed of sound in air v ∝ √T, where T is absolute temperature in Kelvin. T₀ = 0°C = 273 K, v₀ = 332 m/s. T = 27°C = 300 K. Thus v = v₀√(T/T₀) = 332 × √(300/273) ≈ 332 × √1.099 ≈ 332 × 1.048 ≈ 348 m/s ≈ 350 m/s. Approximate rule: speed increases by 0.6 m/s per °C rise, so 27×0.6≈16.2, 332+16.2≈348.2 m/s. Memory aid: 'v ∝ √T in Kelvin'. Such temperature-dependence problems test application of sound wave properties, common in competitive exams with emphasis on absolute temperature usage.

This question belongs to: Science Physics
Question #2
The boiling point of water decreases at high altitudes because
A. Humidity is low
B. Temperature is low
C. Wind speed high
D. Pressure is low

Correct Answer: Option D


Explanation:
Low atmospheric pressure reduces boiling point.

This question belongs to: Science Physics
Question #3
Electron e/m measured by:
A. Millikan
B. Thomson
C. Rutherford
D. Bohr

Correct Answer: Option B


Explanation:
J.J. Thomson measured e/m using cathode ray deflection (1897). Millikan later measured e (oil drop). Memory aid: 'Thomson = e/m; Millikan = e'. Experimental physics history frequently tested in competitive exams.

This question belongs to: Science Physics