Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Why does the direction of light change during refraction if the speed

  1. Oct 7, 2010 #1
    why does the direction of light change during refraction if the speed changes?how are speed and direction related?
  2. jcsd
  3. Oct 7, 2010 #2


    User Avatar
    Science Advisor
    Homework Helper

    welcome to pf!

    hi rahuljayanthb! welcome to pf! :wink:

    it's because light is a wave

    in fact, it applies to any wave … for example, the direction of an earthquake wave will change when it goes through a boundary between rocks with a different speed of sound

    the frequency stays the same (that's obvious, isn't it?), and frequency times wavelength = speed, so if speed decreases, then wavelength must decrease, so the waves must get closer together, and the only way of doing that is to bend away from the perpendicular :smile:
  4. Oct 7, 2010 #3


    User Avatar
    Science Advisor

    Re: refraction

    Just to illustrate what tiny-tim said, here is a video of a simulation (YouTube).

    Notice that the distance between lines in incoming wave (wavelength) is longer than in the wave that passed into material (there is also a reflected wave going back up), but the lines still match at the boundary. That forces a change of the direction angle.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook