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!

Waves, frequency, and power

  1. Dec 28, 2008 #1
    1. The problem statement, all variables and given/known data

    Two identical but separate strings, with the same tension, carry sinusoidal waves with the same amplitude. Wave A has a frequency that is twice that of wave B and transmits energy at a rate that is ____ that of wave B.
    A) half
    B) twice
    C) one fourth
    D) four times
    E) eight times

    2. Relevant equations

    [tex]P = \frac{1}{2}\mu\omega^{2}A^{2}v[/tex]
    [tex]v = \lambda[/tex][tex]f[/tex]

    3. The attempt at a solution

    [tex]V_{B} = \lambda[/tex][tex]f_{B}[/tex]
    [tex]V_{A} = \lambda[/tex][tex](2f_{B})[/tex] = [tex]2V_{B}[/tex]
    [tex]P_{B} = \frac{1}{2}\mu\omega^{2}A^{2}v_{B}[/tex]
    [tex]P_{A} = \frac{1}{2}\mu\omega^{2}A^{2}2v_{B}[/tex] = [tex]2P_{B}[/tex]

    Thus my answer is B.

    However, the answer key says D. What did I do wrong?
  2. jcsd
  3. Dec 28, 2008 #2


    User Avatar
    Science Advisor
    Homework Helper

    If the strings are identical (same mu) and have the same tension, the velocity v is also identical. You can't assume lambda is the same, it can't be. What changes in your power formula is omega. How much does it change?
  4. Dec 28, 2008 #3
    Ah okay, so w = 2pi / f.
    Therefore the Pa = 4Pb.
    Thank you, that makes sense.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Waves, frequency, and power
  1. Waves frequency (Replies: 3)

  2. Frequency of wave (Replies: 0)

  3. Frequencies & Waves (Replies: 10)

  4. Waves and frequency (Replies: 5)

  5. Frequency of a wave? (Replies: 1)