# Snell's Law coursework problem

1. Feb 4, 2006

### RoRo

Hello All,

My child is a student is Florida. She is 14 years old and is enrolled in a Physics class. I was wondering if you guys oculd help me with this question (I am not Physics major)

Based on the diagram above, did the light bend toward or away from the normal as it passed from air into the top of the glass plate?

Rachel.

Last edited: Feb 4, 2006
2. Feb 4, 2006

### RoRo

The Diagra, has now been edited :)

3. Feb 4, 2006

### Ouabache

Welcome RoRo to Physics Forums!! There are young & old here, so please encourage you child to join us, she will undoubtedly find lots of useful and interesting topics across this forum.

The first thing is, she needs to describe what she has thought so far, about the question(s), then we can proceed to steer her in a successful direction. (hint: the answer to this question can be seen in your diagram)
Be sure to read this thread so you will know what is expected of people asking homework questions.

Here is a reference, to get you started.

Last edited: Feb 4, 2006
4. Feb 5, 2006

### RoRo

Thanks a lot for responding. This wasn't really a homework question. It was a review and reflect problem in her text book. Okay she told me to tell you that she knows that "When light slows down, it bends towards the normal, and when it speeds up it bends away from the normal."

She says that what she can't figure out is whether the light rays are speeding up in this diagram...

5. Feb 5, 2006

### Hootenanny

Staff Emeritus
I'll admit that the diagram isn't very good, I can't tell which way the ray is bending. However, you can figure it out logically. Does you daughter know why the light slows down or speeds up?

6. Feb 5, 2006

### RoRo

She says it depends of the refractive index of the period, or so she thinks.

7. Feb 5, 2006

### Hootenanny

Staff Emeritus
So does glass have a higher or lower refractive index than air?
Just looking at the diagram again, you can tell whether the ray bent towards or away from the normal, tell her to look at the ray after it exited the block.

8. Feb 5, 2006

### RoRo

"The galss has a higher refractive index than the air" according to her. She also says that she thinks the ray bends away from the 1st normal, but it bends towards the 2nd.

9. Feb 5, 2006

### Hootenanny

Staff Emeritus
That's the wrong way round. Does she now the mathematical form of snell's law?

10. Feb 5, 2006

### RoRo

No, she doesn't.

11. Feb 5, 2006

### RoRo

She just mentioned something about the co sine of the refractive index over something. She is not 100% sure of the matchematical form. Sorry.

12. Feb 5, 2006

### Hootenanny

Staff Emeritus
Okay, when refraction occurs, the ray leaving the block must be parallel to the ray entering the block. See if that helps.

13. Feb 5, 2006

### Ouabache

Sorry I didn't reply sooner. Just got a chance to see your post again..
Since you know that the glass has a higher refractive index than air, take another look at the first figure in the reference I gave you. It shows a clear direction of the bending relative to the normal. (normal is a perpendicular line or plane with respect to something. In this case with respect to the surface of the glass). It should clarify what you and Hootenanny have discussed.

Just for fun, can you think of an example in nature, where this phenomenon may occur?

Last edited: Feb 6, 2006