5.6- DIFFRACTION

Question 1

What is diffraction?

Answer 1

spreading of waves when they pass through gap or by edge

Question 2

What is the general property of diffraction of all waves very important in?

Answer 2

design of optical instruments, i.e. cameras, microscopes + telescopes

Question 3

What is partly the reason for why we can see features that are not evident when observed directly when looking at planted through a telescope?

Answer 3

partly as less diffraction occurs when waves pass through wide gap than through narrow gap

Question 4

What can diffraction of water waves through a gap be observed by using?

Answer 4

ripple tank

Question 5

What does the ripple tank arrangement show about how diffracted waves will spread out more if…? (2)

Answer 5

gap made narrower, or

wavelength made larger

Question 6

What should close examination of the diffracted wave from the ripple tank arrangement reveal?

Answer 6

each diffracted wavefront has breaks either side of centre

Question 7

What are the breaks at either side of the centre of the diffracted waves from the ripple tank arrangement due to?

Answer 7

waves diffracted by adjacent sections on gap being out of phase + cancelling each other out in certain directions

Question 8

What can diffraction of light by a single slit be demonstrated by?

Answer 8

directing parallel beam of light at slit

Question 9

What does the diffracted light form? (diffraction of light by a single slit)

Answer 9

pattern that can be observed on white screen

Question 10

What does the pattern formed by the diffracted light show? (diffraction of light by a single slit)

Answer 10

shows central fringe with further fringes either side of central fringe

Question 11

Where is the intensity of the fringes the greatest? (diffraction of light by a single slit)

Answer 11

at the centre of the central fringe

Question 12

What is the width of the central fringe in comparison to the outer fringes? (diffraction of light by a single slit)

Answer 12

central fringe twice as wide as each of the outer fringes (measured from minimum to minimum intensity)

Question 13

What does the peak intensity of each fringe decrease with? (diffraction of light by a single slit)

Answer 13

distance from the centre

Question 14

How is each of the outer fringes similar? (diffraction of light by a single slit)

Answer 14

each of the outer fringes is same width

Question 15

What is the intensity of the outer fringes like in comparison to the central fringes?

Answer 15

outer fringes much less intense than central fringes

Question 16

What does the observations show when a single slit pattern is observed using different sources of monochromatic light in turn?

Answer 16

greater the wavelength, the wider the fringes

Question 17

What does the observations show when a single slit pattern is observed using an adjustable slit?

Answer 17

making slit narrower makes fringes wider

Question 18

Equation for the width of the central fringe

Answer 18

W = λ/a * 2D

λ- wavelength of light
a- width of single slit
D- distance from screen to slit

Question 19

What is the width of each fringe proportional to?

Answer 19

λ/a

Question 20

What does the width of each fringe being proportional to λ/a show?

Answer 20

fringes narrower using blue light than if red light had been used

Question 21

In the double slit experiment, where does light pass through and what does it produce?

Answer 21

passes through two slits of double slit arrangement + produces interference pattern

Question 22

What happens if the slits are too wide and too far apart in the double slit experiment?

Answer 22

no interference pattern observed

Question 23

Why is no interference pattern is observed when the slits is too wide and too far apart in the double slit experiment?

Answer 23

interference can only occur if light from two slits overlap

Question 24

How must the slits be in the double slit experiment for interference to happen? (2)

Answer 24

each slit must be narrow enough to make light passing through it diffract sufficiently

two slits must be close enough so diffracted waves overlap on screen

Question 25

Equation for fringe spacing of interference fringes?

Answer 25

w = λD/s

Question 26

Equation for width of central diffraction fringe?

Answer 26

W = 2λD / a