# Homework Help: Snells law

1. Mar 16, 2005

### Novus Dakota

so my given is 1.52 20degrees = 1.10 sin r

im trying to find sin r which comes out to 18.9 degrees but im not sure how find that, can somebody help me out please?

so you do 1.10/1.52

do you divide that into sin 20?

Last edited: Mar 16, 2005
2. Mar 16, 2005

### Jameson

I don't quite understand your notation....

Is that first part : 1.52 * 20 deg?

3. Mar 16, 2005

### Novus Dakota

snells law is n1 sin i = n2 sin r

n1= 1.52
sin i = 20 deg

n2 = 1.10

sin r = ?

sin r actually equals 28.2 deg but i don't understand the process

4. Mar 16, 2005

### Jameson

Isn't this just simple algebra? What do you get when you solve for the unknown variable?

5. Mar 16, 2005

### Jameson

I got 27.6 as my answer...

6. Mar 16, 2005

### Data

.........

$$\sin{x}$$ does not give you an answer in degrees.

$$n_1 \sin{\theta_1} = n_2 \sin{\theta_2} \Longrightarrow \theta_1 = \sin^{-1}\left( \frac{n_2}{n_1} \sin{\theta_2}\right)$$

7. Mar 16, 2005

### Jameson

Isn't the question what is sin r? Not what is the angle...

8. Mar 16, 2005

### Data

Well, in that case he's in for a surprise if he wants it to "come out to $$18.9^\circ$$"

9. Mar 16, 2005

### Novus Dakota

but how do you do it

1.10/1.52 =.723

sin 20=.723

then im stuck....

10. Mar 16, 2005

### Data

Look for the $$\sin^{-1}$$ button on your calculator. Apply it as in the equation I put above.

11. Mar 17, 2005

### K.J.Healey

first calculate sin(20)
then multiply that by 1.52
then divide by 1.10
then take the arcsin/inverse sin of that number
make sure its in degrees and yorue done.

28.2