# Solar Radiation Force

I'm having a little trouble understanding this, mainly the way the maths behind it works. I can't find any kind of derivation on the internet which is 'simple' and at a level I can understand.

My understanding is that the photons from the Sun are absorbed by dust, so transferring momentum from the photon to the 'dust'

I know that

Flux of photons = L/4*pi*r2

I THINK that

Force on a spherical particle of radius a = (pi*a2)*flux*fraction absorbed*force due to a single photon

Is this correct? If it is, what is the force due to a single photon?

Thanks!

## Answers and Replies

Talking about the 'force' of a single photon is not very meaningful. After all, force is something that you continuously apply, the absorption of a photon of course has some duration, but I hve no clue what that would be. What you can calculate is the difference in momentum due to the photon absorption (which is just the momentum of the photon, the constant of Planck divided by its wavelength).

If you would speak of the force of this photon it is just this momentum divided by the duration of the absorption.