3.3.1 Waves

Question 1

How do waves transfer energy?

Answer 1

Without the transfer of matter.

Question 2

c (or v) = ?. What is the worded equation?

Answer 2

fλ. wave speed = frequency x wavelength.

Question 3

Define transverse wave.

Answer 3

The vibration/oscillation is at 90 degrees (perpendicular) to the wav direction.

Question 4

Define longitudinal wave.

Answer 4

Vibration/ oscillation is parallel to the wave direction.

Question 5

Give two examples of transverse waves.

Answer 5

EM spectrum, S-wave earthquakes.

Question 6

Give two examples of longitudinal waves.

Answer 6

Sound, P-wave earthquakes.

Question 7

Define the period of a wave.

Answer 7

The time to create 1 complete wave.

Question 8

How is a stationary wave formed?

Answer 8

When two waves of the same frequency pass through eachother.

Question 9

What is a node?

Answer 9

The point where the waves cancel and there is no displacement.

Question 10

What is an antinode?

Answer 10

The point where the waves interfere constructively.

Question 11

What is the simplest standing wave, what is it referred to as and what is the distance between the nodes?

Answer 11

Your NAN. (Single loop with a node at each end and an antinode in the middle). It is called the fundamental mode of vibration/ fundamental, distance between nodes are 0.5λ.

Question 12

What is the next standing wave from the fundamental and what is it called?

Answer 12

NANAN, second harmonic.

Question 13

Give a 6 mark answer for how a standing wave is formed.

Answer 13

• When the crest of the wave on a string arrives at the far end it reverses phase and is reflected, returning as a trough.
• When it once again reaches the vibrator, it reflects, changes phase and once more becomes a crest.
• This is further reinforced by a new crest leaving the vibrator, then the amplitude is increased.

Question 14

What does raising the tension/ shortening the length do?

Answer 14

Increases the frequency.

Question 15

What does lowering the tension/ increasing the length do?

Answer 15

Lowers the frequency.

Question 16

What is polaroid cellulose film used for?

Answer 16

To reduce glare from reflections.

Question 17

How does polaroid cellulose film reduce glare?

Answer 17

Reflected light is plane polarised, the light is an EM wave so the E-field is reflected in one particular plane. The crystals in the polaroid absorb these waves so the reflection disappears.

Question 18

What sort of waves are polarised, why can’t we polarise other waves?

Answer 18

Transverse waves can be polarised. Can’t polarise longitudinal waves as they can still oscillate through the crystal structure.

Question 19

Which waves show the effect of interference?

Answer 19

All.

Question 20

What does interference rely on and what are some examples?

Answer 20

Relies on waves constructively and destructively interfering. Eg. patterns on a butterfly wing, car paint wraps, oil on water.

Question 21

What happens when waves pass through a small gap? How do we increase the effect?

Answer 21

Diffraction, more diffraction if gap = λ.

Question 22

What happens when we pass waves through two gaps close together?

Answer 22

Waves overlap and cause bright spots.

Question 23

Define constructive and destructive interference.

Answer 23

Crest meets crest, trough meets trough is constructive. Crest meets trough and creates no displacement is destructive.

Question 24

Who said light was a particle, what did he call it?

Answer 24

Isaac Newton, corpuscle.

Question 25

Who said light was a wave?

Answer 25

Christian Huygen.

Question 26

Who proved wave property of light, how? What do we call the nature of light?

Answer 26

Thomas Young in 1801, used double slit experiment. Wave particle duality.

Question 27

What is a coherent wave/ light source?

Answer 27

The waves are in step with eachother.

Question 28

What is Young's double slit equation and what do the letters represent?

Answer 28

λ = ws/D. Fringe separation, w. Slit to screen distance, D. Slit separation, s.

Question 29

What are the equations for constructive and destructive interference using SP and nλ?

Answer 29

Constructive S1P - S2P = nλ | Destructive S1P-S2P = (n + 1/2)λ

Question 30

How do we order the beams in the diffraction grating experiment?

Answer 30

Central = 0 order beam. 1st, 2nd etc. symmetrically outwards from 0.

Question 31

How does diffraction pattern change with λ?

Answer 31

Angle of diffraction between each beam and the zero order beam increases with increasing λ.

Question 32

How does diffraction pattern change with slit difference?

Answer 32

The angle of diffraction between each beam and the 0 order beam increases with decreasing gap size.

Question 33

What is the equation for diffraction gratings?

Answer 33

nλ = dsinθ. θ is angle between zero order and 1st, 2nd etc order.

Question 34

How do you work out the slit separation for a grating of 300 lines/mm?

Answer 34

d = 1/N. d = 1/300x10^3

Question 35

Angle of incidence = ?. What law is this?

Answer 35

Angle of reflection. Law of reflection.

Question 36

Define refraction.

Answer 36

The change in direction of a wave due to its speed. Most commonly seen when a wave passes from one medium to another medium of different optical densities.

Question 37

What is TAGAGA?

Answer 37

Towards (normal) Air Glass Away (normal) Glass Air.

Question 38

Where does light bend when travelling from less to more optically dense materials and vice versa?

Answer 38

Towards is less to more. Away is more to less.

Question 39

When light is parallel to the normal what happens to refraction?

Answer 39

Doesn't apply, since ray continues along the normal.

Question 40

What is n? What is the equation? Who's law is this?

Answer 40

n is the refractive index. n = SinI/SinR. Snell's law.

Question 41

Define refractive index.

Answer 41

Measure of the bending of a ray of light when passing from one medium to another (relative to a vacuum).

Question 42

When i < C what happens with the refraction?

Answer 42

Away from normal.

Question 43

When i = C what happens with the refraction?

Answer 43

Refracts along the boundary at 90 degrees to normal.

Question 44

When i > C what happens with the refraction?

Answer 44

TIR.

Question 45

If you send light back along the boundary at 90 degrees to the normal what is r?

Answer 45

r = C.

Question 46

What is the equation for C?

Answer 46

C = sin^-1(1/n)

Question 47

Define C.

Answer 47

The critical angle is the angle at which the emergent ray is refracted along the boundary between the two materials (i.e. the angle of refraction is 90 degrees).

Question 48

What are fibre optics and what do we use them for?

Answer 48

'Wire for light', TIR carries light from one end of the wire to another. Eg. medical endoscopes, fibre optic communication.

Question 49

Where does TIR take place in a fibre optic cable?

Answer 49

At the core-cladding boundary.

Question 50

What are the refractive indexes of the core and cladding?

Answer 50

Cladding is lower than core.

Question 51

What do we make the core to reduce absorption?

Answer 51

Optically clear.

Question 52

Why is cladding needed?

Answer 52

To prevent cross talk from one channel to another, prevents damage to the core.

Question 53

What do we do to the core to reduce multipath dispersion?

Answer 53

Thin.

Question 54

Why are fibre optics used for high speed data communication?

Answer 54

``` Immune to EM interference. No electrical current, no heating. Lower losses per unit length, allows longer distances between repeater amplifiers. No corrosion. Higher bandwidth, more data transmitted. ```

Question 55

Define progressive wave.

Answer 55

Transfers energy from one point to another without transferring material/matter.

Question 56

What is the equation for frequency?

Answer 56

f = 1/T

Question 57

With waves of the same amplitude but higher freq. explain the effect on an amp/distance graph.

Answer 57

Smaller λ, smaller spread in main peak/more peaks, central peak is higher, because energy conc. over smaller area.

Question 58

Explain how a bright line is formed by the diffraction grating at the 1st order diffraction angle.

Answer 58

Light from each slit superpose, light from adjacent slits have a path difference of 1 λ, all waves are in phase, constructive interference.

Question 59

How do you calculate 1st order diffraction angle?

Answer 59

sinθ = λ/d

Question 60

How do you calculate highest order observed?

Answer 60

``` n = d sinθ/λ n(max) = d sin90/λ ```