# Determining the the index of refraction

1. Oct 31, 2016

### kubajed

1. The problem statement, all variables and given/known data
I must determine the refractive index of the adhesive tape. Tools I can have is: laser, tape, carton, scissors etc.
I don't know how to do it.

2. Relevant equations
n=c/v
n=sin alfa/sin beta

3. The attempt at a solution
I tried a lot of configurations to observe something but without effect

2. Oct 31, 2016

3. Nov 1, 2016

### kubajed

I can't use any tools except that I wrote in first post.

4. Nov 1, 2016

### Merlin3189

Perhaps you could tell us about the methods you have tried?

I've never done this and don't know the answer.
I'd have thought about other experiments to measure thin layers.
Since you have a laser, I'd also try to think of how refractive index might affect a laser beam.

5. Nov 1, 2016

### Staff: Mentor

But using the link posted by @Bystander and related links at wikipedia like this one:

https://en.wikipedia.org/wiki/Refractive_index

What kinds of things could you try to do to get the laser passing through the tape to give you something useful...?

6. Nov 1, 2016

### kubajed

I tried to get stripes on carton. But it doesn't work.

7. Nov 1, 2016

8. Nov 1, 2016

### kubajed

Stripes like using diffraction grating, but it was stupid. I know that outgoing beam is moved in comparison to incoming beam. But the problem is small thickness of tape.

9. Nov 1, 2016

### Staff: Mentor

So can you think of ways you could amplify the small displacement from the thin dielectric layer? How transparent is the tape?
In addition to diffraction, what other property of light is affected by a change in the dielectric constant as the light beam transitions from one medium to another?

10. Nov 1, 2016

### Staff: Mentor

Can you post a picture of the tape, or link to the product? There is another trick that you can use to get around the thinness of the tape sample...

Like: https://images-na.ssl-images-amazon.com/images/I/41wtuh6hckL._SY355_.jpg

11. Nov 1, 2016

### kubajed

I can use a lot of connected layers but transparency is so low then.

12. Nov 1, 2016

### Staff: Mentor

That picture holds the key to the trick I was thinking of. Did you ever see the old Star Trek movie "The Wrath of Khan"?

13. Nov 1, 2016

### kubajed

No, I didn't

14. Nov 1, 2016

### Staff: Mentor

Fair enough. I'm trying to think of a way to give you a hint for the trick, without just giving it straight away...

Here is the quote I was going to refer to to try to get you to think differently about the problem...

15. Nov 1, 2016

### kubajed

Do you suggest to experiment with 3D?

16. Nov 2, 2016

### kubajed

Could you tell me a little bit more?

17. Nov 2, 2016

### Staff: Mentor

Not exactly. The point is to think of other geometries that you could use to take care of the problem of having such a thin sample.

18. Nov 2, 2016

### Staff: Mentor

Back when I was in high school, I found a short book on problem solving (I wish I could remember the title). It gave lots of tips and tricks for solving all kinds of problems, as well as general techniques for ways to think about problems. One of the best tips was when you were presented with a difficult problem that had obstacles to its solution, think about ways to turn things around up upside-down or some other way (physically or conceptually) to see if those alternative views gave any clues to ways to get past the obstacles.

I believe that I came up with a good trick for you to use to do this experiment, and I used that tip from the book on problem solving to get to it. Hope that helps.

19. Nov 2, 2016

### sophiecentaur

When you learn about refractive index, there is something else that can happen when a light ray passes from one medium to another, other than just bending the ray. Go about a page beyond the first page in the book.

20. Nov 2, 2016

### kubajed

The laser beam is also reflected. It is it?