Critical Angle

1. Dec 14, 2012

Molly1235

Hello,

I would really appreciate some help with this question as my understanding of the topic is not that great, so trying to decipher the answer from the notes in my textbook is not easy. This is Edexcel GCSE Physics P3.

"Draw and label a diagram to show how you could use prisms...
A) to see round the corner of a building
B) to see a reflection of yourself"

I know this has something to do with critical angle but I really don't understand what. The only thing I can think is that you need a reflection to change the light so it goes around the corner, but then another for it to come back for you to see it? And I have no clue for part b!

Would be appreciative of some guidance.
Thanks :-)

2. Dec 14, 2012

haruspex

Have you heard of total internal reflection? Do you understand what that looks like in terms of light rays through a prism, and how it relates to critical angle?

3. Dec 14, 2012

Molly1235

Yes, I know of total internal reflection, but can't quite connect this to critical angle and the prism in my head?

4. Dec 14, 2012

haruspex

Total internal reflection means a surface of the prism can act as a mirror, but only for light coming from within the prism. So the trick is to have the light from the source enter the prism square on, then reflect of a surface at an angle, and exit the prism square on to the third surface.
Total internal reflection will occur if the angle of incidence exceeds the critical angle (which is why it's called critical). This will depend on the medium.
Having discovered how to make a prism behave like a mirror, you can then arrange several to achieve the objectives.