1. Limited time only! Sign up for a free 30min personal 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!

Find the frequency of the wave

  1. Oct 2, 2009 #1
    1. The problem statement, all variables and given/known data
    A 550 nm harmonic wave whose electric field is in the z direction is traveling in the y direction in vacuum.

    a)find the frequency of the wave
    b)determine [tex]\omega[/tex] and k.
    c)if the electric field amplitude is 600 V/m find the amplitude of the magnetic field.
    d)write an expression for both E(t) and B(t) given that each is zero at x=0 and t=0.

    2. Relevant equations

    3. The attempt at a solution
    I've solved all the other questions but part d is giving me a bit of trouble.

    [tex]\Psi[/tex](0,0)=Acos(0) + Csin(0)
    0=A(1) + C(0)
    therefore A=0 but not necessarily C so i wrote
    E(t)=[tex]\hat{y}[/tex]Csin(kx-[tex]\omega[/tex]t) and

    This is the part I'm stuck on, I'm unsure on how to solve for the constant C, the amplitude of the function.

    *edit the formatting is a bit off, it should be kx-wt, the w isn't a power of anything.
  2. jcsd
  3. Oct 2, 2009 #2


    User Avatar
    Homework Helper
    Gold Member

    First, [itex]\textbf{E}(\textbf{r},t)=C_E\sin(kx-\omega t)\mathbf{\hat{y}}[/itex] describes an electric field, with amplitude [itex]C_E[/itex], polarized in the [itex]y[/itex]-direction, and traveling in the [itex]x[/itex]-direction....that isn't what the problem statement you've posted asks you to describe....
  4. Oct 3, 2009 #3
    Thank you for the quick reply. Since my idea is wrong, could you give me a hint on the correct way to solve the problem.
  5. Oct 3, 2009 #4


    User Avatar
    Homework Helper
    Gold Member

    Remember, the general form of a plane wave, traveling along the direction of [itex]\mathbf{k}[/itex] and polarized in the [itex]\mathbf{\hat{n}}[/itex] direction is [itex]\textbf{E}(\textbf{r},t)=C\sin(\mathbf{k}\cdot\textbf{r}-\omega t)\mathbf{\hat{n}}+D\cos(\mathbf{k}\cdot\textbf{r}-\omega t)\mathbf{\hat{n}}[/tex]

    What would you expect [itex]\mathbf{\hat{n}}[/itex] to be if the field is polarized in the [itex]z[/itex]-direction?

    What would you expect [itex]\mathbf{k}\cdot\textbf{r}[/itex] to be if the field is traveling in the [itex]y[/itex]-direction?
    Last edited: Oct 3, 2009
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Find the frequency of the wave
  1. Frequency of waves? (Replies: 2)

  2. Find frequency. (Replies: 1)