# Homework Help: Electromagnetic Waves (concept)

1. Sep 22, 2009

### calvert11

1. The problem statement, all variables and given/known data
Given the electromagnetic wave traveling in the y direction at velocity c:

B = +cEo sin(k y − ω t) ˆi.

a) What happens to the ratio of the electric to magnetic field if the angular velocity ω of the
wave is decreased? Does it decrease, increase, or remain the same?

b) What happens to the velocity of the wave if the angular velocity ω of the wave is decreased? Does the velocity decrease, increase, or remain the same?

c) What happens to the the wavelength of the wave if the angular velocity ω of the wave is
decreased? Does the wavelength decrease, increase, or remain the same?

2. Relevant equations

E/B = v
v= ω/k
λ/c = 2*π/ω

3. The attempt at a solution

a) My guess: Since v= ω/k, decreasing ω would decrease v. So, if E/B = v, and v is decreasing, E/B also decreases. I think the ratio decreases. (INCORRECT)

b) My guess: Since v=ω/k, velocity decreases as ω decreases. I think the velocity decreases.

c) My guess: Wavelength is inversely related to angular velocity by λ/c = 2*π/ω. So, if angular velocity decreases, the wavelength increases. I think the wavelength increases.

2. Sep 22, 2009

### kuruman

All electromagnetic waves in vacuum travel at the speed of light c regardless of their frequency or wavelength. Start from there and reconsider your answers.