Rays and Waves

Question 1

Give the formula for refractive index.

Answer 1

r = speed of light in vacuum / speed of light in medium
r = sini/sinr

Question 2

What are the characteristics of the image in front of the principal focus of a convex lens?

Answer 2

1. upright
2. magnified
3. virtual

Question 3

What is a virtual image?

Answer 3

An image that cannot be picked up on a screen, because the rays never converge to meet it.

Question 4

What are the characteristics of an image formed behind the principal focus?

Answer 4

1. inverted
2. x cm high
3. x cm from the lens
4. real

Question 5

Explain why light may not bend when passing into a glass block.

Answer 5

May be travelling along the normal at 90 degrees, so angle of incidence is 0.
This means that the wavefront all slows down at the same time.