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NTA Abhyas 2020

Exam: NTA Abhyas
Year: 2020
Subject: Physics
Chapter: Electromagnetic Waves

NTA Abhyas 2020 · Physics · Electromagnetic Waves

A totally reflecting small plane mirror placed horizontally faces a...

A totally reflecting small plane mirror placed horizontally faces a parallel beam of light as shown in the figure. The mass of the mirror is

200g

. Assume that there is no absorption in the lens and that

20 %

of the light emitted by the source goes through the lens. The power of the source needs to support the weight of the mirror is

P \times {10}^{8}watt

, where

P

is [take

g = 10m{s}^{- 2}

]

A totally reflecting small plane mirror placed horizontally faces a parallel beam of light as shown in the figure. The

Correct answer

15

Step-by-step solution

mg = \dfrac{2P}{C}

{P}^{'} = \dfrac{200 \times 1{0}^{- 3} \times 10 \times 1{0}^{8} \times 3}{2}

P ‘ = 300 \times {10}^{6} = 300MW

P = \dfrac{{P}^{'}}{0.2} = 1500 \times 1{0}^{6} = 15 \times 1{0}^{8}W

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