# Homework Help: Direction of Electric Field in an Electromagnetic Wave

1. Apr 24, 2015

### spaghetti3451

1. The problem statement, all variables and given/known data

If the magnetic field of a light wave oscillates parallel to a y axis and is given by $B_y = B_m\ sin(kz- \omega t)$,

(a) in what direction does the wave travel and

(b) parallel to which axis does the associated electric field oscillate?

2. Relevant equations

3. The attempt at a solution

(a) The wave is propagating in the $+ z$-direction because the form of the argument in the sinusoidal function.

(b) I'm having problem here.

2. Apr 24, 2015

### Simon Bridge

(b) where are you having the problem?

3. Apr 24, 2015

### spaghetti3451

I think I figured it out. :D

If the direction of propagation is given by $\overrightarrow(E) \times \overrightarrow(B)$, then shouldn't the direction of the electric field be in the $+ x$-direction.

4. Apr 24, 2015

### Simon Bridge

That's the one - well done.
Just remember that the E and B fields are perpendicular.

LaTeX note: use curly brackets to enclose what you operate on, but not needed if there is only on letter following the command.
Thus \vec E \times \vec B gets you $\vec E \times \vec B$

5. Apr 25, 2015

### spaghetti3451

Thank you! :)