SP5

Question 1

What are rays?

Answer 1

Lines that show the direction in which waves travel.

Question 2

What is the relation between wavefronts and rays?

Answer 2

Rays are always perpendicular to wavefronts.

Question 3

How does the angle of incidence correlate with the angle of refraction?

Answer 3

As the angle of incidence increases, so does the angle of refraction (but not proportionally).

Question 4

What is a critical angle?

Answer 4

A specific angle of incidence where the refracted light passes along the interface, and no light passes on the side where the less dense medium is.

Question 5

What is total internal reflection?

Answer 5

It is when the angle of incidence becomes greater than the critical angle, then the light is completely reflected inside the glass.

Question 6

How do we test for internal reflection?

Answer 6

1. Place a semicircular glass block on a large sheet of paper and draw around it.
2. Remove the block. Using a ruler and pencil, find and mark the center of the straight side.
3. Draw a normal line through this point, perpendicular to the straight side, then replace the block.
4. The ray will bend away form the normal as it leaves the glass and some light is reflected by the straight surface of the glass block.
5. Move the ray to increase the angle of incidence, which increases the angle of refraction. Continue increasing the angle of incidence until the reflected ray lines up with the flat surface of the block.
6. Increase the angle of incidence again. The light is now reflected completely, no light escaping by refraction (total internal reflection). The angle of incidence at which total internal reflection begins is the critical angle.