1. Limited time only! Sign up for a free 30min personal 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!

Race between light rays

  1. Mar 17, 2014 #1
    Imagine two light rays parallel to each other , one of them is traveling in vaccum and the other one in water. We place a detector at the same distance from the source and fire the two rays inside their respective media.who will win the race? Or is it possible to have a tie in the competition?
  2. jcsd
  3. Mar 17, 2014 #2


    User Avatar
    Gold Member

    Can you Google "speed of light in vacuum" and "speed of light in water" ???
  4. Mar 17, 2014 #3
    Oh sorry I am a really dumb kid who can make a new thread but can't Google something.
    I did do it but wasn't satisfied by the results, some places they said that the light ray travels with the absolute velocity but with a phase shift and so I wanted to know if that could result in actual delay in traversing a geometric path.
  5. Mar 17, 2014 #4
    Light speed in water is about 75% of vacuum light speed.
  6. Mar 17, 2014 #5


    User Avatar

    Staff: Mentor

    Since we get a lot of that here, it is helpful to provide that information upfront. We can't provide the appropriate help if we don't know where you are.
  7. Mar 18, 2014 #6


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    Phase lag, at a given frequency, and time delay are effectively the same thing. In the case of light frequencies, there could be a pretty massive phase shift over a long path. It is quite possible to detect two 'racing' pulses when they arrive at different times, even over a few metres of 'race track. 3 X10^8 m/s is a very 'finite' quantity.

    Lenses all work on the principle that the phase / time shift through the thick parts of the glass is greater than the air+glass path through the thin parts.

    I could suggest that you try to hone your searching skills. What you read may not immediately strike you as useful but is worth while making the effort to make sense of it - or use another link. It is all too easy to ask questions and all too easy for them to be mis-interpreted. PF is much more useful for sorting out individual points than as an education system. Books are incredibly good as a source of total learning.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook