The prefix 'femto' in SI units represents a factor of: MCQ with Answer and Explanation

The prefix 'femto' in SI units represents a factor of:
A. 10⁻¹²
B. 10⁻¹⁸
C. 10⁻¹⁵
D. 10⁻⁹
Answer: Option C
Solution (By JKSSB Mock Tests)
The SI prefix 'femto' denotes a factor of 10⁻¹⁵. This is standardized by the International Bureau of Weights and Measures. Common prefixes: pico (10⁻¹²), femto (10⁻¹⁵), atto (10⁻¹⁸), nano (10⁻⁹). Femtometer (10⁻¹⁵ m) is used in nuclear physics to measure atomic nuclei sizes. Exam tip: Remember the sequence: pico, femto, atto for decreasing scales. This question tests fundamental knowledge of SI prefixes essential for unit conversions in competitive examinations.

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Practice More Physics Questions

Question #1
A lens which is thicker at center and thinner at edges is
A. Plano-concave
B. Cylindrical
C. Convex
D. Concave

Correct Answer: Option C


Explanation:
Convex lens converges light, thicker centre.

This question belongs to: Science Physics
Question #2
A piece of copper wire has resistance 10 Ω at 0°C. α = 0.004/°C. At 100°C resistance is
A. 14 Ω
B. 12 Ω
C. 10 Ω
D. 8 Ω

Correct Answer: Option A


Explanation:
R_t = R₀(1+α t) = 10(1+0.004×100) = 10(1.4) = 14 Ω.

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Question #3
A machine does 500 J of work in 10 seconds. Its power is
A. 5000 W
B. 0.5 W
C. 50 W
D. 5 W

Correct Answer: Option C


Explanation:
Power = work/time = 500/10 = 50 W. Watt = Joule/second. This is average power. Simple division. Higher power means faster rate of doing work.

This question belongs to: Science Physics