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

Understanding wavelength and frequency.

  1. Jan 22, 2010 #1
    "when light enters from one medium to other its frequency remains same whereas wavelength changes."
    i'm not able to understand this relation as frequency has a inverse relation to wavelength
    please help me to understand it thoroughly.
     
  2. jcsd
  3. Jan 22, 2010 #2

    f95toli

    User Avatar
    Science Advisor
    Gold Member

    Yes, but what IS the relation between frequency and wavelength?
    Have you looked at the formula?
     
  4. Jan 22, 2010 #3
    frequency is inversely proportional to wavelength
    and thats where my problem is if wavelength changes how come the frequency remains constant.
     
  5. Jan 22, 2010 #4
    wavelength * frequency = speed

    If frequency remains the same and wavelength changes, then speed must change (this isn't a statement of causality, it's just a look at the equation). Light has different speeds in different mediums so it makes sense that it could change.
     
    Last edited: Jan 22, 2010
  6. Jan 22, 2010 #5
    i understand, why can't it happen other way frequency changes and wavelength remains same. (and this is what i was pondering about :))
     
    Last edited: Jan 22, 2010
  7. Jan 22, 2010 #6
    Good question! I would be interested in the answer too. I have learned that frequency is determined by the source and wavelength by the medium, but I have not learned why each of those properties are tied to each of those factors.
     
  8. Jan 22, 2010 #7

    f95toli

    User Avatar
    Science Advisor
    Gold Member

    Well, one "handwaving" argument is that the energy of light is proportional to frequency (E=h*f) and since energy has to be conserved it is the wavelength that must change.

    I am sure one can think of a simpler reason, but this is probably as good as any.

    Also, remember that -as with everything in physics- this is ultimately an experimental fact, we do know that light travels at different speed in different media, and we also know the if we send in a wave with a given frequency into a medium the wavelength changes whereas the frequency does not.
     
  9. Jan 22, 2010 #8
    i was jus trying to picturise the statement
    "when light enters from one medium to other its frequency remains same whereas wavelength changes."
    http://en.wikipedia.org/wiki/Frequency see the first right hand diagram titled
    by using defeniton of wavelength (one crest & one trough) i'm not able to conceptualize the idea of frequency remaining same and wavelength changes.
     
  10. Jan 22, 2010 #9
    The reason the frequency has to be constant when crossing a boundary is because a frequency is a count of individual events, which are, in this case, cycles. It's like if you have birds flying through an open window at a rate of ten per minute, that rate as counted from the outside and that rate as counted from the inside have to be the same.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Understanding wavelength and frequency.
Loading...