# Δp for total reflection and absorbtion of E&M radiation explanation?

by Phyzwizz
Tags: Δp, absorbtion, eandm, explanation, radiation, reflection
 P: 54 The equation for the change in momentum for total absorption of electromagnetic radiation is ΔU/c and that for total reflection is (2ΔU)/c. How could the momentum of electromagnetic radiation change if it is massless and travels at a constant speed c? Is the ΔU just a representation of a change in the frequency of the radiation? Also my book does a poor job in explaining the reason that the change in momentum is double for total reflection (perhaps this will become more clear with an explanation of the previous questions).Δ
 P: 1,506 The change in momentum for reflection is 2 x thechange for absorption for the same reason that the change in momentum for a ball hitting a wall and stopping dead is mv but a ball rebounding with the same speed has a change in momentum of 2mv. Momentum changes from +mv to -mv.
 P: 6 Complete Reflection Δp = ΔU/c - (-ΔU/c) = 2(ΔU/c)

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