# Homework Help: Electromagnetic Wave

1. Apr 10, 2007

### Zonda

1. The problem statement, all variables and given/known data
A plane electromagnetic wave, which is polarized in the positive y-direction, propagates in the negative z-direction. What is the direction of the magnetic field of this wave?

2. Relevant equations
My choices are:

+z direction.
-y direction.
-x direction.
+y direction.
+x direction.
-z direction.

3. The attempt at a solution

I don't understand polarization much. Also, from what I know about electromagnetic waves the magnetic and electric fields point in two directions so I can't just answer one answer it would have to be two of the choices above but I don't have that option.

2. Apr 10, 2007

### G01

HINT: Magnetic field components of a E-M wave, will be at right angles to the electric field components.

3. Apr 11, 2007

### Zonda

So, from what I can gather, the answer is +x or -x, it can be either one can't it?

4. Apr 11, 2007

### Zonda

Nevermind. I got it and it was positive x. How is that so, though? I swear it can be both positive and negative x. I even drew it out!

5. Apr 11, 2007

### Mentz114

The equation that connects the direction of travel (k) and the directions of the E and B fields is -

$$\vec{k} = \vec{E} \times \vec{B}$$

That's a vector cross product - see here http://mathworld.wolfram.com/CrossProduct.html