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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 200 g . 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 × 10 8 watt , where P is [take g = 10 m s - 2 ]

Correct answer

15

Step-by-step solution

m g = 2 P C P ' = 200 × 1 0 - 3 × 10 × 1 0 8 × 3 2 P ‘   =   300   ×   10 6   =   300   MW P = P ' 0.2 = 1500 × 1 0 6 = 15 × 1 0 8   W

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