Unit 2.5: Wave properties

Question 1

Define Refraction

Answer 1

The change in direction of a wave at the boundary between two materials. This is caused by a change in speed.

Question 2

Define Diffraction

Answer 2

The spreading of a wave when it meets an obstacle into regions where it would not be seen if it moved only in straight lines

Question 3

Define reflection

Answer 3

As the waves strike a plane (flat) barrier they are reflected

Question 4

What happens if waves are reflected off a curved barrier?

Answer 4

If a curved (concave) barrier such as a satellite dish is used, the waves can be made to converge (concentrate) at a point.

Question 5

Do waves move slower in deep or shallow water?

Answer 5

The waves move more slowly in shallow water.
The frequency of
the waves remain constant and so the wavelength decreases.

Question 6

Young’s Double slits: Does greater diffraction occur if there is a greater distance between the slits or smaller distance?

Answer 6

The smaller the distance between the slits, large diffraction occurs.

Question 7

State the principle of superstition

Answer 7

The principle of superposition states if the waves from two sources occupy the same region then the total displacement at a point is the vector sum of the displacements of the individual waves at that point.

Question 8

There are two types of interference, what are they?

Answer 8

Constructive and destructive

Question 9

What is constructive interference?

Answer 9

If they arrive at a point in phase they will interfere constructively. If the two
incoming waves have the same frequency and equal amplitude A, the resultant wave produced by constructive interference has an amplitude 2A.

Question 10

What is destructive interference?

Answer 10

If the two waves are out of phase that is they will interfere destructively. If the waves have equal
amplitude, the resultant wave has zero amplitude.

Question 11

What is coherence?

Answer 11

To observe interference the two wave sources must be coherent and get a meaningful resultant wave by using the principle of superposition.

Question 12

What is coherent?

Answer 12

there is a constant phase
difference. (They must therefore have the same
frequency)

Question 13

What did Young’s double slit experiment prove?

Answer 13

That light travels as waves

Question 14

What is path difference

Answer 14

A measure of the distance between two waves arriving at a point in
terms of their wavelength.

Question 15

What is young’s double slit experiment

Answer 15

When interference from two coherent sources occurs a pattern of
bright and dark fringes appears

Question 16

What can Young’s double slit experiment be used to determine?

Answer 16

The wavelength of light.

Question 17

State the equation for Young’s slits experiment

Answer 17

λ=aΔy/D
λ=wavelength
a=distance between slits
Δy=fringe spacing
D=distance from the slits to the screen

Question 18

What is a diffraction grating?

Answer 18

A diffraction grating is a plate on which there is a very large number of parallel, identical, very closely spaced slits. If monochromatic light is incident on this plate, a pattern of narrow bright fringes is produced.

Question 19

Are Double slits the same as a diffraction grating?

Answer 19

Double slits are not the same as a diffraction grating

Question 20

On a diffraction grating, what are bright fringes caused by?

Answer 20

Constructive
interference. Therefore,
at a bright point the phase
difference from the different slits is equivalent to an integer number of wavelengths

Question 21

State the equation to calculate wavelength from a diffraction grating

Answer 21

nλ=dSinθ
d=slit width
n=order number
λ=wavelength
θ=angle

Question 22

Why are the bright fringes usually further apart in a diffraction grating than Young’s slits?

Answer 22

Because there are so many slits, the bright fringes (or bands) are extremely narrow, and usually much
further apart (large ‘y’ since slit separation, ‘d’ is very small).

Question 23

Explain Young’s double slit experiment

Answer 23

Two light sources at the double slits are
produced. Because these two light sources
originate from the same primary source,
they are coherent and create a sustained
and observable interference pattern of the dark and bright interference fringes.

Question 24

During a Young’s double slits experiment, what causes bright fringes and what causes dark fringes?

Answer 24

Bright fringes=Constructive interference
Dark fringes=destructive interference

Question 25

Diffraction grating with white light, what colour is diffracts the most and what colour diffracts the least?

Answer 25

Red light, because it has the longest wavelength in the spectrum, is diffracted through the largest angle.
Violet light has the lowest wavelength, and
is diffracted the least.

Question 26

What is a stationary wave?

Answer 26

A stationary wave is a pattern of disturbances in a medium, in which energy is not propagated. The amplitude of particle oscillations is zero at equally-spaced nodes, rising to maxima at
antinodes, midway between the nodes.

Question 27

How is a stationary wave created?

Answer 27

Stationary waves are produced from the superposition of two progressive
waves of equal amplitude and frequency, travelling in opposite directions.

Question 28

On a stationary wave the amplitude at nodes are equal to what?

Answer 28

0

Question 29

On a stationary wave the amplitude at antinodes is equal to what?

Answer 29

The maximum amplitude

Question 30

A standing wave creates what musical note?

Answer 30

the 4th harmonic

Question 31

Phase between the nodes is what?

Answer 31

Phase between the nodes is constant. Even though their amplitude is different.

Question 32

What is the difference between each node?

Answer 32

½λ

Question 33

Phase changes by pi at the nodes