7. Diffraction

Question 1

What is diffraction?

Answer 1

The way that waves spread out as they come through a narrow gap or go round obstacles

Question 2

What does the amount of diffraction depend on?

Answer 2

The wavelength of the wave compared with the size of the gap

Question 3

What happens when the gap is a lot bigger than the wavelength?

Answer 3

Diffraction is unnoticeable

Question 4

What happens when the gap is several wavelengths wide?

Answer 4

Diffraction is noticeable

Question 5

When does the most diffraction happen?

Answer 5

When the gap is the same size as the wavelength

Question 6

What happens when the gap is smaller than the wavelength?

Answer 6

The waves are mostly just reflected back

Question 7

What is meant by the shadow?

Answer 7

Where the wave is blocked by an obstacle

Question 8

What causes a long shadow?

Answer 8

A wider obstacle than the wavelength of the wave

Question 9

How can you observe a clear diffraction pattern?

Answer 9

Use a monochromatic, coherent light source

Question 10

What is monochromatic light?

Answer 10

Light of a single wavelength and frequency and so is a single colour

Question 11

What happens if you use light that isn’t monochromatic for observing diffraction patterns?

Answer 11

Different wavelengths will diffract different amounts and the pattern produced won’t be very clear

Question 12

What are laser lights?

Answer 12

A monochromatic and coherent light source

Question 13

Describe the pattern of single-slit diffraction for a laser light

Answer 13

1. Has light and dark fringes

2. The central fringe is the brightest

Question 14

What are the bright fringes a result of?

Answer 14

Constructive interference where waves from across the width of the slit arrive at the screen in phase

Question 15

What are the dark fringes a result of?

Answer 15

Total destructive interference where waves from across the width of the slit arrive completely out of phase

Question 16

Describe the pattern of single-slit diffraction for a white light

Answer 16

1. The central fringe is white
2. The light fringes are a spectrum of colours with red being the furthest from the centre because of their longer wavelength

Question 17

Define the term intensity?

Answer 17

Intensity is the power per unit area

Question 18

What is meant by the intensity of light?

Answer 18

The number of photons per unit area per second

Question 19

What 2 things affect the width of the central maximum?

Answer 19

1. Width of the slit

2. Wavelength of the light being diffracted

Question 20

What happens to the width and intensity of the central maximum when the slit width increases?

Answer 20

The central maximum is narrower as a result of the lower amount of diffraction causing the intensity to be higher

Question 21

What happens to the width and intensity of the central maximum when the wavelength increases?

Answer 21

The central maximum is wider as a result of the higher amount of diffraction causing the intensity to be lower