Light year is unit of: MCQ with Answer and Explanation

Light year is unit of:
A. Distance
B. Speed
C. Time
D. Luminosity
Answer: Option A
Solution (By JKSSB Mock Tests)
Light year: distance light travels in one year in vacuum ≈ 9.46×10¹⁵ m. Astronomical distance unit, not time. Memory aid: 'Light year = speed × time = distance'. Unit knowledge frequently tested in competitive exams to avoid common misconception about light year being time unit.

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Practice More Physics Questions

Question #1
If the error in the measurement of the momentum of a particle is +100%, what will be the percentage error in the measurement of its kinetic energy?
A. 200%
B. 300%
C. 400%
D. 100%

Correct Answer: Option B


Explanation:
Kinetic Energy (K) is given by K = p^2 / 2m. If momentum (p) increases by 100%, the new momentum is p' = p + 1.0p = 2p. The new kinetic energy is K' = (2p)^2 / 2m = 4(p^2 / 2m) = 4K. The increase is 4K - K = 3K. Percentage increase = (3K/K) * 100 = 300%.

This question belongs to: Science Physics
Question #2
Newton's contribution to physics:
A. Electromagnetic theory
B. Theory of relativity
C. Quantum mechanics
D. Laws of motion and gravitation

Correct Answer: Option D


Explanation:
Isaac Newton: three laws of motion, universal gravitation, calculus, optics. Relativity: Einstein; EM theory: Maxwell; Quantum: Planck/Bohr. Memory tip: 'Newton = classical mechanics foundation'. Scientist-discovery association frequently tested in competitive exams.

This question belongs to: Science Physics
Question #3
A 100 W bulb operates at 220 V. The current drawn by it is approximately:
A. 4.5 A
B. 0.45 A
C. 0.22 A
D. 2.2 A

Correct Answer: Option B


Explanation:
Electric power P = VI. Thus I = P/V = 100 W / 220 V ≈ 0.4545 A ≈ 0.45 A. This direct application of power formula is fundamental in electricity. Memory tip: 'I = P/V for resistive loads'. Competitive exams frequently test such calculations with household appliance ratings. Always use consistent units (watts, volts, amperes). Note: This assumes purely resistive load (valid for incandescent bulbs); for motors or electronics, power factor may matter, but not at this level.

This question belongs to: Science Physics