# Electromagnetic Wave

#### Zonda

1. Homework Statement
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. Homework 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.

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#### G01

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

#### Zonda

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

#### 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!

#### Mentz114

Gold Member
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