Diffraction

Question 1

What does diffraction control?

Answer 1

The detail you can see in optical instruments.

Question 2

What is diffraction?

Answer 2

The spreading out of light from it’s geometrically defined path.

Question 3

What is the underlying cause of diffraction?

Answer 3

The addition of waves from a continuous line or surface of sources.

Question 4

When does diffraction occur?

Answer 4

When the wavefront of an advancing wave is partially blocked by an apeture.

Question 5

In the case of Fraunhofer diffraction what are the two simplifying approximations made?

Answer 5

1. If the source is at infinity-plane waves
2. If the pattern is at infinity- There is a small apeture.

Question 6

What happens at the first minima?

Answer 6

Light from the middle of the slit is lambda/2 out of phase with light from the top. The lower half light cancels out with the top half.

Question 7

What happens at the first maximum?

Answer 7

Light from the first third is cancelled by light from the second third, leaving the final third.

Question 8

What happens at the second minimum?

Answer 8

At the second minimum light from the first quarter is cancelled out by light from the second quarter and the same for the next two quarters.