SI unit of luminous intensity: MCQ with Answer and Explanation

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SI unit of luminous intensity:

A. Candela

B. Lux

C. Lumen

D. Watt

Answer: Option A

Solution (By JKSSB Mock Tests)

Candela (cd) is SI base unit for luminous intensity. Lumen: luminous flux; Lux: illuminance; Watt: power. Memory aid: 'Candela = candle power; base unit for perceived light'. Unit knowledge frequently tested in competitive exams.

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Question #1

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A car moving with speed 20 m/s applies brakes and stops in 5 s. The distance covered during braking is

A. 100 m

B. 200 m

C. 25 m

D. 50 m

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Correct Answer: Option D

Explanation:
u=20, v=0, t=5, a = (0-20)/5 = -4 m/s². s = ut + ½at² = 20×5 + ½×(-4)×25 = 100 - 50 = 50 m. Or average velocity = (20+0)/2 = 10 m/s, distance = 10×5 = 50 m.

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Question #2

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According to Newton's Law of Cooling, the rate of loss of heat from a body is strictly proportional to:

A. The square of the temperature of the body.

B. The fourth power of the temperature difference.

C. The temperature difference between the body and its surroundings.

D. The absolute temperature of the surroundings.

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Correct Answer: Option C

Explanation:
Newton's Law of Cooling is a practical approximation stating that the rate of heat loss of a body is directly proportional to the difference in temperatures between the body and its immediate environment, provided this temperature difference is relatively small. The equation is dQ/dt = -k(T_body - T_surroundings).

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