# Homework Help: Physics HELP!

1. Jan 27, 2009

### patriots1049

1. The problem statement, all variables and given/known data
1. What property of light causes the sunlight to reach the earth before the sun actually appears over the horizon?

2. What is the wavelength, in water, of blue light whose wavelength is 4.5 x 10^2 nm in air?

3.The speed of a certain liquid in a certain liquid is 3/4 the speed in a vacuum. What is the index of refraction of the liquid?

4. A clear plastic material has an index of refraction of 1.9. Light of frequency 4.5 x 10^14 Hz enters the plastic. What is the wavelength of the light while it is in the plastic?

5. A ray of light enters a piece of glass, making an angle of 50.0 degrees with the surface. What angle does the refracted ray make with the surface?

6. What is the index of refraction of a type of plastic for which the critical angle is 40.0 degrees.

2. Relevant equations

Our teacher gave us this, with no information.

3. The attempt at a solution

I need some formulas or a step in the right direction.

2. Jan 27, 2009

### LowlyPion

3. Jan 27, 2009

### patriots1049

Anyway someone could walk me through some of these problems?

Last edited: Jan 28, 2009
4. Jan 27, 2009

### patriots1049

Last edited: Jan 28, 2009
5. Jan 27, 2009

### LowlyPion

6. Jan 27, 2009

### patriots1049

1. I think number 1 has to deal with the electromagnetic waves being refracted.

2. I know I do 3.0 x 10^8 * .700 to get the speed of light in water. Then I'm stuck.

3. The speed is 2.25 x 10^8, but I don't know how to get the index of refraction.

4. I am really lost.

5. 50 degrees as well?

6. Is it 1.54? sin(40) = .64 1/1.54 = .64

7. Jan 27, 2009

### LowlyPion

1. Photons, EM waves ... sounds ok.

2. If the wave is moving slower, what happens to the wavelength? You know how much slower, so what frequency do you get as a result?

3. What is the index of refraction? Have you looked it up?
http://en.wikipedia.org/wiki/Refractive_index#Definitions

4. Same method as 2.

5. See the Snell's Law link I posted earlier.

6. Yes. Close enough to 1.56.