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Homework Help: What Is the frequency of red light?

  1. May 10, 2017 #1
    1. The problem statement, all variables and given/known data
    The speed of light in a vacuum is 3.00x(10*8)m/s. Using the equation v=fxλ, calculate the frequency of red-light. (I was told to use the wavelengths given from textbook)
    Wavelength/λ =700nm

    v=300,000,000 <-- ( I need help understanding this. Is this a rate? Or?)
    2. Relevant equations
    700nm = 0.00000070 meters.
    ^ This is what I'm confused on, do i convert this then plug it into the equation or? I'm also confused on how to plug it in.
    3. The attempt at a solution
    v= 3x(10*8)=300,000,000
    f= 300,000,000/0.00000070=4.2857143*14 <-- I understand this is the wrong answer, however I'm terribly confused as to how to find the correct one. Even looking at examples, I don't understand what's converted and how to go about answering it.
    Thank you.
  2. jcsd
  3. May 10, 2017 #2


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    Hi Daniel Kh and welcome to PF.

    How do you know the answer is wrong? It looks OK to me.
  4. May 10, 2017 #3
    That is the speed of light. Light travels at 300,000,000 meters per second (m/s). (Actually, if I remember correctly, I think the exact speed of light is 299,792,458 m/s.) So if your answer of 4.2857143 x 10^14 is wrong, you may want to consider trying a more exact value for the speed of light.

    Also, if your answer is being check by some computer system, I could see how an answer of 4.2857143*14 could be considered wrong (if that is exactly how it was entered) - unless the asterisk is interpreted by that software to be exponential notation. It reads as if you are multiplying 4.2857143 times 14.
    I would have written it 4.2857143*10^14, if I was using Excel, for example. That may just be a typo on this posting, but I was just trying to think of different ways that your answer could be considered incorrect.
  5. May 10, 2017 #4
    Thanks guys!
    I'm just confused on how to put that down? Do i include the power of 14? And yes, the asterick was a typo, i meant the "^".
    Do I just write it has a frequency of 4.3^14?
    Or should I write out the long zeroes..?
    The reason I assumed it was wrong is that when i googled It, i found answers about it being something around 500Hz and that threw me off.
    Should I just put 4.3 as a whole and add "Hertz" or "Hz" at the end?
    Sorry for the confusion!
  6. May 10, 2017 #5
    That is incorrect also. That is 4.28 to the 14th power.
    Maybe you could try 4.28e14. That is fairly standard.

    Edit: That is standard notation for 4.28 x 10^14.
  7. May 10, 2017 #6
    Ah I see.
    I solved It.
    Thanks a ton guys! I now see Physics is very very specific.
    Thanks again!
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