2.5 - Wave properties

Question 1

What is reflection?

Answer 1

As the waves strike a plane (flat) surface they are reflected. If curved (concaved) barrier is used the waves can be made to converge (concentrate) at a point

Question 2

In reflection the angle of incidence and reflection will be _____

Answer 2

equal

Question 3

What is refraction?

Answer 3

Is the change in direction of a wave at the boundary between 2 materials. This is caused by change in speed

Question 4

What is diffraction?

Answer 4

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

Question 5

When the λ is much smaller than the gap width, there is _____ diffraction and the main beam spreads out through less then ___

Answer 5

little
180

See NC1

Question 6

When the λ is ______ than or equal to the gap width, the beam spreads out in approx semi-circular wave fronts ( so has spread out through _____)

Answer 6

greater
180

Explains why we can hear sound round corners but cannot see round them. The λ of light is to small compared to the gap (e.g. door), whereas the λ of sound comparable to it

See NC1

Question 7

What does the principal of superstition say?

Answer 7

The resultant waves displacement at a time is given by the sum of the 2 individuals displacements (taking note of + and - displacements

Question 8

If 2 waves arrive together at a point in phase, that is if their crests arrive at exactly the same time, they will interfere __________. If the two
incoming waves have the same ________ and equal ________ A, the resultant wave produced by constructive interference has an amplitude 2A. The frequency of the resultant wave is the
same as that as the incoming waves.

See NC 2

Answer 8

constructively
frequency
Amplitude

Question 9

What is 2 source interference?

Answer 9

Is when waves from 2 different sources superpose and form a new wave. The 2 waves need to have the same frequency. The amplitude of this resultant wave depends on how the two waves meet

Question 10

if the two waves are out of phase that is, if the peaks of one wave arrive at the same time as the troughs from the other, they will interfere ____________. The resultant wave will have a ________ amplitude.

Answer 10

destructively
smaller

See NC2

Question 11

What does coherent mean?

Answer 11

Means that there is a constant phase difference. (They must therefore have same f)

Question 12

Give examples of coherent and incoherent light sources

Answer 12

A laser (coherent light source).
Car headlights, normal light bulb (incoherent light source).

Coherent sources are monochromatic with wavefronts continuous
across the width of the beam and, (when comparing more than
one source) with a constant phase relationship.

Question 13

What is path difference?

Answer 13

The measure of the distance between 2 waves arriving at a point in terms of there wavelength

Question 14

When the 2 rays meet on the screen, they either undergo ________ or ________ interference

Answer 14

constructive
destructive

Question 15

For constructive interference, the PHASE difference needs to be integer multiple of ___ but as ___ is one whole wave cycle we say that the PATH difference needs to be an integer multiple of the wavelength = ___

Answer 15

2 pi
2 pi
nλ

Refer to NC 3

Question 16

Why is it easier to measure max and min distances when a beam is shone through a diffraction grating then in Youngs experiment with 2 slits?

Answer 16

A diffraction grating has more slits so the shaper the pattern. A diffraction grating has smaller slit separation which means that the beam spreads further apart.

Question 17

What is a coherent source?

Answer 17

Sources which are monochromatic (of only one wavelength) and have constant phase difference. They have wave fronts continuously across the width of the beam. Which means that you could travel from one side of the beam to the other across 1 wave front

Question 18

Give examples of coherent and incoherent light sources?

Answer 18

Laser - coherent
Filament lamps - incoherent because of the random electron transitions between atoms causing changes in phase difference

Question 19

Give the 2 main conditions for 2 source interference?

Answer 19

Sources must be coherent
Oscillations must be in same direction

Question 20

What are stationary waves?

Answer 20

Waves which store energy instead of transferring energy like progressive waves do.

Question 21

How are stationary waves formed?

Answer 21

When you have 2 waves of equal frequency and amplitude traveling in opposite directions which superpose creating a sequence of nodes and antinodes

Question 22

The nodes are where there is __ _________ and the anti nodes are where there is ___ ____________. The distance between adjacent nodes = λ/2

Answer 22

no movement
max displacement/ oscillation

Question 23

If the path S1P = length of path S2P ( in the centre) then that means the 2 waves arrive at P in phase. So we get _________ interference

If the path difference S2P - S1P = nλ or integer multiples of this
The the waves arrive in ____ at P so ________ interference

If the path difference S2P -S1P = λ/2 or multiples of this
Then the waves arrive in __________ at P so _________ interference

Answer 23

constructive
phase
constructive
anti-phase
destructive

See NC 4