7

If a photon hits a 'perfect' mirror (with no environment interference) would the mirror move a bit?

Brandon Enright
  • 11,937
user128932
  • 379
  • If a photon hits a perfect mirror that is fixed and rigid would the photon 'rebound' faster than if the mirror was not fixed? – user128932 Jun 13 '14 at 18:14

2 Answers2

13

Yes. Actually photons exert pressure on any surfaces exposed to them. For example, photons emitted by the Sun exert pressure of $9.08 \mu N/m^2$ on the Earth.

Reference: https://en.wikipedia.org/wiki/Radiation_pressure

Qianyi Guo
  • 933
  • How much acceleration would that be, for example for a 1×1 meter square object with a mass of 1 gram in meters per second square? – user1306322 Apr 12 '14 at 11:45
  • @user1306322: Just use good old F=ma and of course force = pressure * area to work it out. – Chris Apr 12 '14 at 13:41
  • 1
    $a=\frac{F}{m}=\frac{9.08\mu N}{1g}=9.08\times 10^{-3} m/s$. That's a quite small acceleration so in order to build a practical spaceship powered by solar radiation, we need a quite large solar sail. In addition, this estimate doesn't consider solar wind but that's several orders of magnitude weaker. – Qianyi Guo Apr 12 '14 at 14:43
  • Does a photon exerting pressure cause the photon itself to loose some energy in some fashion? Is any of the energy of a photon hitting a surface absorbed by the surface and if so does this deplete some of the photons energy? Is all the energy of a photon independent of its movements? – user128932 Apr 15 '14 at 06:08
  • See https://en.wikipedia.org/wiki/Radiation_pressure#Radiation_pressure_by_particle_model:_photons – Qianyi Guo Apr 15 '14 at 09:13
8

Yes - you can even propel spaceships with it - Solar Sail

Although Solar radiation pressure at the Earth is around 9E-6N/m2 while the thrust from a Saturn V rocket is 34 MN, so you would need a solar sail something like 2000Km on a side to get the same acceleration

Martin Beckett
  • 30,766