Light year is unit of: MCQ with Answer and Explanation

Light year is unit of:
A. Luminosity
B. Time
C. Distance
D. Speed
Answer: Option C
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
A boy throws a ball vertically upward with velocity 20 m/s. Time after which ball returns to his hands (g=10) is
A. 1 s
B. 8 s
C. 2 s
D. 4 s

Correct Answer: Option D


Explanation:
Total time = 2u/g = 40/10 = 4 s.

This question belongs to: Science Physics
Question #2
An electric heater of resistance 10 Ω draws current 5 A. Power consumed is
A. 500 W
B. 50 W
C. 2 W
D. 250 W

Correct Answer: Option D


Explanation:
P = I²R = 5² × 10 = 25 × 10 = 250 W. Also P = VI, but V not given. Can find V = IR = 50 V, then P = 50×5 = 250 W.

This question belongs to: Science Physics
Question #3
Photon energy E = hν. For higher frequency light, photon energy is:
A. Lower
B. Higher
C. Same
D. Zero

Correct Answer: Option B


Explanation:
E ∝ ν: higher frequency ⇒ higher photon energy. Gamma rays (high ν) more energetic than radio waves (low ν). Memory aid: 'E = hν; blue light photons more energetic than red'. Quantum physics relation frequently tested in competitive exams.

This question belongs to: Science Physics