Question:
derivation of the expression for force exerted by a EM wave
Answer:
When electromagnetic radiation hits a particular surface, force is exerted on the surface by radiation.
We know that Pressure = Force /Area. Here it is radiation pressure of the electromagnetic wave.
Case 1 : If the radiation is completely absorbed by the surface then radiation pressure = Average intensity Iavg / speed of light = Iavg / c
P = F/A (Area hit by light radiation) = Iavg / c
Hence, F = Iavg / c * A (Area hit by light radiation)
Case 2 : If the surface completely reflects the light, then P = F/A = = 2Iavg / c
Hence, F = 2Iavg / c * A (Area hit by light radiation)
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