Questions on LIGHT?

Question 1

1. Briefly describe Huygens’ wave theory of light.

Answer 1

Huygens’ wave theory of light
Huygens suggested that light was a longitudinal wave
capable of propagating through a material called the aether
which he believed fills all space. This material medium
justified why light can pass through a vacuum despite the
fact that it was supposedly a longitudinal wave, as is sound.

Question 2

2. Which scientist proposed a particle theory of light?

Answer 2

Newton proposed a particle theory of light.

Question 3

3. a. Which theory of light was backed by the experiment performed by Young?
   b. How does Young’s experiment support the theory mentioned in part a?

Answer 3

a) The wave theory was supported by Young’s experiment.
b) Young’s experiment produces an interference pattern of bright and dark fringes from two coherent sources of light.

Interference is a phenomenon of waves.

The bright fringes occur where the waves meet in phase and the dark fringes occur where they meet exactly out of phase.

Question 4

4. a. Which theory was backed by the experiment performed by Foucault?
   b. How does Foucault’s experiment support the theory mentioned in part a?

Answer 4

a) The wave theory was supported by Foucault’s experiment.
b) Foucault’s experiment proved that light travels faster in the air than in water.

This is contrary to the expectations of particle theory, which suggest that it should travel faster in water.

Question 5

5. a. Name TWO 20th-century scientists responsible for the quantum theory?
   b. What does the quantum theory suggest?

Answer 5

Planck and Einstein are the scientists responsible for the quantum theory.

b) The quantum theory suggests that light can be considered as being a particle and wave-like in nature.

Each wave pulse can be considered as a packet (particle) of energy.

Question 6

6. a. What is meant by the term diffraction?
   b. What condition is required for strong diffraction?
   c. Why is the diffraction of light waves not generally observed?

Answer 6

ok

Question 7

7. a. What is meant by the term interference?

Answer 7

ok

Question 8

8. This question is about Young’s double-slit experiment.
   a. Why is it not possible to use two separate lamps as the light sources?
   b. Why is it not possible to use a source of white light without a colour filter if complete destructive interference is to be observed?
   c. What can you say about the path difference between waves that produce a bright fringe on the screen?

Answer 8

ok