# Homework Help: Constant frequency for light waves?

1. Apr 3, 2005

### thursdaytbs

"what is the frequency of red light in the air? What is the frequency of red light in the glass?"

is the frequency of a light wave length constant? therefore, the answer would be the same?

2. Apr 3, 2005

### whozum

The speed of a light wave through vacuum, air and glass is not the same due to some refraction effects. Try finding these speeds of light through those mediums and compute the frequency with those speeds.

3. Apr 3, 2005

### ShawnD

Correct, frequency never changes. When light slows down in high refractive index materials, only the wavelength changes.
Suppose you have light going from air to a material n=2. The velocity is going from x to 0.5x. Wavelength decreases at the same rate as the velocity (since wavelength and velocity are directly proportional), so if the original wavelength was $\lambda$, the new wavelength is 0.5$\lambda$. Frequency stays the same as it was before.

4. Apr 4, 2005

### quasar987

A way to remember might be to consider that if frequency were to change, then according to

$$E = h\nu$$

it would mean the energy changes as well. That would be a little too weird.

5. Apr 4, 2005

### primarygun

So wavelength is the critical factor which determine the colour of a wave but not other factors, such as frequency, right>?

6. Apr 4, 2005

### ShawnD

That's right.