# Homework Help: Electromagnetic wave problem

1. Apr 9, 2016

### JesseJC

1. The problem statement, all variables and given/known data
⃑E = Eo cos(4.0y−1.2 × 109 t) ̂ (N/C)
where y is in meters and t is in seconds. The intensity of the wave is 200 mW/cm2 .

(a) In what direction is the wave propagating? (b) What are the wavelength and frequency of the wave? (c) What is the peak value of the electric field, 0, of the wave? (d) Find the magnetic field, ⃑⃑⃗(⃗,), of the wave. (e) Find an expression for the Poynting vector ⃑⃗(⃗,)

2. Relevant equations

3. The attempt at a solution
Do not know where to begin with this one, I cannot find any useful help related to anything similar to this question online, not even in my professors lectures. If anyone can just help me begin here I would appreciate it greatly. I understand the E-field is going in the x direction, but how can I visualize that? I also understand that the propagation is ExB.

2. Apr 10, 2016

### drvrm

try writing expression of electric field as solution to electromagnetic field equations and try interpreting your given equation above'
ask when E is maximum ?
when its at minima?
what is the wavelength,frequency....

3. Apr 10, 2016

### Staff: Mentor

Why do you say that? I don't see any x in your equation. Or have you left something out? I'm wondering about that ^ near the end, just before the units.