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## Homework Statement

Radiation of intensity

*I*is normally incident on an object that absorbs a fraction

*frac*of it and reflects the rest back along the original path. What is the radiation pressure on the object?

## Homework Equations

Radiation pressure Pr (force/unit area)

Pra = I/c (total absorption)

Prr = 2I/c (total reflection back along path)

## The Attempt at a Solution

The object absorbs a fraction

*frac*of the intensity, which I translate mathematically as:

Pra = (frac)*I / c

This would mean that the total intensity reflected is:

Prr = 2*(1 - frac)*I/c

Unfortunately the answer is: Pra = (2 - frac)*I / c

I don't know how they came to this conclusion. Thanks in advance, MrMoose