A plane electromagnetic wave of intensity 6.1 W/m^2 strikes a dark surf ace of a

Question

A plane electromagnetic wave of intensity 6.1 W/m^2 strikes a dark surf ace of area 73 cm^2 perpendicular to the approaching wave and is completely absorbed. Find the force that the wave exerts on the mirror on picoNewton. Enter an integer. A light source radiation isotropically in all directions. The intensity at a distance 0.41 m from the center of the source is 83 W/m^2. What is the intensity at a distance 1 02 m from its center in W/m^2? Enter a number with one digit behind the decimal point.

Explanation / Answer

Question 1 )

The wave is reflected by the mirror. The momentum transferred to the mirror per unit area per second is twice the momentum of the light striking the mirror per unit area per second.

dp/dt = 2*1/c * S*A

S*A = 6.1 x 73 x 10^-4 = 0.04453 W

dp/dt = 2*0.00453/3*10^8 = 2.97 x 10^-10 N

dp/dt = F = 3 x 10^-10 N

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