1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Calculate the total momentum of the photons

  1. Jun 8, 2008 #1


    User Avatar

    1. The problem statement, all variables and given/known data
    The solar sail uses “radiation pressure” caused by the momentum of photons of sunlight as they strike the sail. A sail with an area of [itex]1.5 \times 10^6 m^2[/itex] could be used to propel a spacecraft of mass [itex]1.2 \times 10^3 kg[/itex].
    The energy [itex]E[/itex] and momentum [itex]p[/itex] of a photon are related by the expression [itex]E = pc[/itex], where [itex]c[/itex] is the speed of light.
    Calculate the total momentum of the photons striking [itex]1 m^2[/itex] of sail in one second. Assume the solar radiation flux (intensity) is [itex]1400 W m^{-2}[/itex].

    2. Relevant equations

    3. The attempt at a solution
    Can I have hint's on how to approach this.

    The momentum eqaution that I know is [itex]p=mv[/itex] but I don't think I can use this. :confused:
  2. jcsd
  3. Jun 8, 2008 #2
    If you multiply intensity by the area of the sail the units cancel to leave watts which is Joules per a second. Then if you multiply the intensity by the area you will get 1400W considering it is 1m(squared). Since the aircraft is in space any force is going to propel it so all you have do from here is find how Watts relates to momentum and you're set. Hope this helps.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Calculate the total momentum of the photons
  1. Total Momentum (Replies: 4)

  2. Total Momentum (Replies: 1)

  3. Momentum of a photon (Replies: 9)