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Homework Help: Working out how many complete waves are sent out.

  1. Nov 14, 2012 #1
    1. The problem statement, all variables and given/known data
    A source of light emits a train of waves lasting 0.04 μs. The light has a wavelength of 600nm and the speed of light is 3×108ms-1. How many complete waves are sent out?

    2. Relevant equations
    f=v/wavelength (sorry, I couldn't find the wavelength symbol)


    3. The attempt at a solution
    Ok, this is what I tried:


    then I did:


    Which was so close to one of the answers; frustrating! Could somebody please explain to me what to do? It's driving me crazy. I'm finding it hard to carry on with the rest of the assignment because I keep going back to that question and staring at it, willing my brain to work!
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Nov 14, 2012 #2

    You entered this into the calculator wrong. Watch your parenthesis.

    A big clue that something is wrong is that you have a period of 2000 s. If light has a really small wavelength and a fast speed, does it make sense that it should take over half an hour for one wave cycle?
  4. Nov 14, 2012 #3
    Thank you! I now get the answer 2×107.
    Yeah, I did look at the 2000s and think that was a tad wrong...
    I'm now torn between being pleased that I knew how to work out the answer and the dismay of not being able to use a calculator.
    Thank you again!
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