x Turn on thread page Beta
 You are Here: Home >< Physics

# Angle of incidence watch

1. Resolved
2. First calculate the angle of reflection to help you calculate i

Angle of incidence = angle of reflection.

Angle of reflection = 85

Angles in a triangle

i = 180 - (30 + angle of reflection)
i = 180 - (30 + 85)
i = 180 - 115
i = 75o

Then use refractive index = (sin(angle of incidence))/(sin(angle of refraction)) to calculate r

use 1.41 for refractive index as that is the substance the light is entering.

1.41 = (sin(75))/(sin(r))

rearrange and solve for r

sin(r) = (sin(75))/1.41
r = sin-1 (sin(75))/1.41
r = 43.24o

I would have put solution in spoiler if I knew how. Sorry.

I hope I was able to help.
3. resolved

But for question 2 the mark scheme says you are wrong.

It is using this formula n1sini=n2sinr

How will I be able to distinguish which formula to use?

Because I too did use the same formula as you and was hoping whether someone can tell me why.

Ah. I think we have to use the formula that they stated because the light ray is present in the core with refractive index which is not equal to the one of air, 1. the formula I used might only work when light is going from air into another substance.

I've never seen that formula before.

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: April 14, 2013
Today on TSR

### I have imposter syndrome at Cambridge

Poll

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE