1. Not finding help here? Sign up for a free 30min 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!

Figuring out wavelength

  1. Mar 15, 2015 #1
    1. The problem statement, all variables and given/known data
    1)The frequency of a wave is 4.0 x 10^7Hz. What is its wavelength?

    2. Relevant equations
    V= wavelength times frequency
    f=1/T

    3. The attempt at a solution
    1. Okay so I'm using the calculator on my iPod and I'm aware I'm supposed to use EE in some manner but don't know how.
     
    Last edited by a moderator: Mar 15, 2015
  2. jcsd
  3. Mar 15, 2015 #2

    berkeman

    User Avatar

    Staff: Mentor

    What is the speed of light in m/s?
     
  4. Mar 15, 2015 #3
    Straight from google;

    299 792 458
     
  5. Mar 15, 2015 #4

    berkeman

    User Avatar

    Staff: Mentor

    Put it into scientific notation so it is easier to do the calculation -- Use your equation "V= wavelength times frequency" and be sure to show units for each quantity...
     
  6. Mar 15, 2015 #5
    That's the weird thing. It's shown as 3 straight numbers so are those spaces supposed to be commas? Like 200,000,000?
     
  7. Mar 15, 2015 #6

    berkeman

    User Avatar

    Staff: Mentor

    Roger that. So just re-write it as 2.99792448 * 10^__ [m/s] and set up your equation to solve...
     
  8. Mar 15, 2015 #7
    Okay, that's 8 but where exactly is the speed of light supposed to fit into the equation?
     
  9. Mar 15, 2015 #8

    berkeman

    User Avatar

    Staff: Mentor

    Well, if it's a wave with a frequency in the THz range, that's pretty much guaranteed to be EM radiation. That would travel at the speed of light in a vacuum. Do you have any reason to believe it is traveling in a dielectric that would slow it down?
     
  10. Mar 15, 2015 #9
    I'm not saying I don't believe you but it's weird that none of this is in the formulas given to me.
     
  11. Mar 15, 2015 #10

    berkeman

    User Avatar

    Staff: Mentor

    Yes it is. You listed it as a relevant equation already (see above quote). V [m/s] = Wavelength [m] * Frequency [1/s = Hz]...
     
  12. Mar 15, 2015 #11
    Nowhere on my sheet does it mention a completely other number that is supposed to relate to the equation I'm solving.
     
  13. Mar 15, 2015 #12
    Anyway, am I dividing speed of light by the frequency of the wave?
     
  14. Mar 15, 2015 #13

    berkeman

    User Avatar

    Staff: Mentor

    Yep, that's how you use that relevant equation. See how the units work out?

    I have to bail for a couple hours. I'll check your answer when I get back. :smile:
     
  15. Mar 15, 2015 #14
    Can anyone confirm if the answer is 749,481,120,000,000 ?
     
  16. Mar 15, 2015 #15

    vela

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Education Advisor

    As one of my colleagues would ask, "749,481,120,000,000 cows? Wow, that's a lot of cows."

    The other comment I have is if you multiply that by the given frequency, would you get the speed of light?
     
  17. Mar 15, 2015 #16
    I think so, but theres a lowercase "e" with a +21 at the end
     
  18. Mar 15, 2015 #17

    vela

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Education Advisor

    You might want to rethink that. The frequency is a pretty big number, and the wavelength you got is in the hundreds of trillions. Think about how big the product would be. Now while light travels fast, does it travel that fast? (The answer is no.) Can you come up with an estimate of how big the answer should be?
     
  19. Mar 15, 2015 #18
    It is a ridiculously big number so should the 0's end at 120?
     
  20. Mar 15, 2015 #19

    vela

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Education Advisor

    Try the calculation without using scientific notation.
     
  21. Mar 15, 2015 #20

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    I guess the context makes it clear that we have an electromagnetic wave in vacuum? That should be given somewhere.

    @berkeman: We have MHz, not THz.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Figuring out wavelength
Loading...