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Homework Help: Having trouble with these problems

  1. Sep 19, 2005 #1
    hey guys idk how you know all this stuff, and id appreciate if you helped me. i have to do wavelength and and frequency problems and i dont really understand how to do it the way my teacher taught it, so here they are and thanks for helping me.

    1.The frequency of yellow light is 5.5 x10^14 Hz. Find the wavelength of yellow light. The speed of light is 300 000 km/s.

    2.AM radio signals are broadcast at frequencies between 570 kHz and 1580 kHz (kilohertz) and travel 3.0 x10^8 m/s.

    (a) What is the range of wavelengths for these signals? (Enter the wavelengths from shortest to longest.)
    ____m to ______ m
    (b) FM frequencies range between 88 MHz and 108 MHz (megahertz) and travel at the same speed. What is the range of FM wavelengths?
    ______ m to _____ m

    3.The velocity of a wave on a string depends on how hard the string is stretched, and on the mass per unit length of the string. If FT is the tension in the string, and ยต is the mass/unit length, then the velocity, v, can be determined.
    heres a pic of the formula i have to use

    A piece of string 5.30 m long has a mass of 17.0 g. What must the tension in the string be to make the wavelength of a 120 Hz wave 120.0 cm?

    thanks again
    Last edited: Sep 19, 2005
  2. jcsd
  3. Sep 19, 2005 #2


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    What is the basic relationship between wavelength, frequency and speed?

    Look at the units of each of those quanities, see if you figure out a way to combine them that gives you the units you need.
  4. Sep 19, 2005 #3
    i really have no idea about any of these, they become way too confusing, i know that you can use frequency and wavelength to get speed, but thats about it
  5. Sep 19, 2005 #4


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    You're definately on the right track. Now check your text to see what it says about them. Once you note that relationship (hint: it is linear expression), you can find your solutions. (Curious, what grade is this being presented?)
    Last edited: Sep 19, 2005
  6. Sep 19, 2005 #5


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    Speed is distance over time, yes? And wavelength is...? And the relationship between frequency and time is...? You really should be able to figure it out from there even without the book.
  7. Sep 19, 2005 #6
    Check out the units.

    Wavelength = meters
    Speed of light = meters DIVIDED by seconds
    Frequency = 1 DIVIDED by seconds

    write these down on a piece of paper and try to figure it out from there... what are you trying to get?
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