Question

A totally reflecting, small plane mirror placed horizontally faces a parallel beam of light as shown in figure (42-E1). The mass of the mirror is 20 g. Assume that there is no absorption in the lens and that 30% of the light emitted by the source goes through the lens. Find the power of the source needed to support the weight of the mirror. Take g = 10 m/s².

Answer 1

m = 20 g

The weight of the mirror is balanced. Thus force exerted by the photons is equal to weight

=> Rate of change of momentum = Power/C

30% of light passes through the lens.

Thus it exerts force. 70% is reflected.

 Force exerted = 2(rate of change of momentum)

Comments

rate of change of momentum= power/c kaise hua..??? plz explain

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Already explain in the above