Calculating Refraction: Snells Law Help for Light Ray Approaching Glass Block

[Sprattboy]

Snells law -- help please

A light ray approaches a glass block at 30° to the normal. The refractive
indices of air and water are 1 and 1.5 respectively At what angle will the light
be refracted? This uses Snells law

I did Sin 30 / Sin r = 1 / 1.5
I then multiplied both sides in order to get rid of sin 30.
After that, I got Sin r = 1/1.5(xSin30)
This gave me an answer of -1.48
When I do inverse sine it gives me an error
What did I do wrong?

 

[SammyS]

A light ray approaches a glass block at 30° to the normal. The refractive
indices of air and [STRIKE]water[/STRIKE] glass (?) are 1 and 1.5 respectively At what angle will the light
be refracted?


This uses Snells law

I did Sin 30 / Sin r = 1 / 1.5
I then multiplied both sides in order to get rid of sin 30.
After that, I got Sin r = 1/1.5(xSin30)
This gave me an answer of -1.48
When I do inverse sine it gives me an error
What did I do wrong?

Check your algebra !

 

[Sprattboy]

Check your algebra !

I have

 

[TheAustrian]

Check it again and again, just to be sure, a minus answer should be rather unlikely in elementary examples.

 

[TheAustrian]

I did Sin 30 / Sin r = 1 / 1.5
I then multiplied both sides in order to get rid of sin 30.
After that, I got Sin r = 1/1.5(xSin30)

You did your fractions wrongly.

You should have got this:

\frac{1}{sin(r)}=\frac{1}{1.5(sin(30))}

 

[dauto]

Make sure your calculator is set for degrees instead of radians. You're getting a negative sign because you're using radians. That's what happens when you blindly follow the calculator without a clue of what to expect. You end up eating calculator garbage.

 

[adjacent]

What dauto said. and:

Since you have done that,(Did it using radians), be sure to reset your calculator especially before exams.