Flashcards in Diffraction Deck (25):

1

## When does diffraction occur?

### Diffraction occurs when waves spread out after passing through a gap or around an obstacle.

2

## What are some features of diffraction?

###
• The narrower the gap, the more the waves spread out.

• The longer the wavelength the more the waves spread out.

3

## What is diffraction?

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

4

##
What does the amount of diffraction depend on?wavelengths wide.

• Most diffraction occurs when the gap is the same size as the wavelength

###
The amount of diffraction depends on the wavelength of the wave compared with the size of the gap.

• When the gap is bigger than the wavelength, diffraction is unnoticeable.

• Noticeable diffraction occurs through a gap several wavelengths wide.

• Most diffraction occurs when the gap is the same size as the wavelength

• If the gap is smaller than the wavelength, the waves are mostly reflected back.

5

## What happens when the gap is bigger than the wavelength?

###
Diffraction is unnoticeable.

6

## When do you get noticeable diffraction?

### • Noticeable diffraction occurs through a gap several wavelengths wide.

7

## When does the most diffraction occur?

### • Most diffraction occurs when the gap is the same size as the wavelength

8

## What happens if the gap is smaller than the wavelength?

### • If the gap is smaller than the wavelength, the waves are mostly reflected back.

9

## What is required to view a clear diffraction pattern for light?

### You need a monochromatic, coherent light source.

10

## What does monochromatic mean?

### All the light has the same wavelength and frequency, and also therefore is the same colour.

11

## Why do waves diffract?

###
• Each point on a wavefront is a secondary emitted of wavelets.

• The wavelets from the point along a wavefront travel only in the direction in which the wave is travelling, not in the reverse direction.

• They then combine to form a new wavefront spreading beyond the gap.

12

## What is a wavefront?

### A wavefront is a line or surface, in the path of a wave motion, where all the displacements at any point have the same phase

13

## What is the central maximum?

###
• The central maximum in a single slit light diffraction pattern is the brightest part of the pattern.

• This is because the intensity of light is highest in the centre.

14

## What is the formula for the width of the central fringe?

###
Width of the central fringe = ( Wavelength of the light / Width of the Single Slit ) x 2 D

• D = Distance from the slit

15

## What happens if the single slit pattern is observed using different sources of monochromatic light?

###
Using different sources of monochromatic light:

The observations show that the greater the wavelength the wider the fringes

16

## What happens if the single slit pattern is observed using an adjustable slit?

### observations show that making the slit narrower makes the fringes wider.

17

## What happens if the slits are too wide and too far apart in young's experiment?

###
No interference pattern is observed, this is because interference can only occur if the light from the two slits overlaps, for this to be the case:

• Each Slit must be narrow enough to make the light passing through it diffract sufficiently

• Two slits must be close enough so the diffracted waves overlap on the screen.

18

## What is required for interference to occur?

###
interference can only occur if the light from the two slits overlaps, for this to be the case:

• Each Slit must be narrow enough to make the light passing through it diffract sufficiently

• Two slits must be close enough so the diffracted waves overlap on the screen.

19

## For monochromatic light, incident on two slits, what is the formula for for fringe spacing of the interference fringes?

###
W = wavelength x screen distance from the slit / s

S = slit separation

W = λ x D / S

20

## What is the formula for the width of the central diffraction fringe?

###
W = 2 x λ x D / a

D = slit-screen distance

21

## What is intensity?

### Power per unit area

22

## What does increasing the light do for monochromatic light and why?

###
• For monochromatic light, all photons have the same energy

• An increase in intensity means an increase in the number of photons per second.

• There are more photons per unit area hitting the central maximum per second than the other bright fringes.

23

## What two factors affect the width of the central maximum?

###
• Slit width

• Wavelengeth

24

## How does slit width affect width of the central maximum?

###
• Increasing the slit width decreases the amount of diffraction.

• This means the central maximum is narrower, and the intensity of the central maximum is higher

25