C11/12 - Waves 1 & 2

Question 1

What’s a progressive wave?

Answer 1

An oscillation that can travel through matter or sometimes a vacuum.
The particles move from their equilibrium position to a new position. The particles in the medium exert forces on each other. A particle experiences a restoring force which pulls it back to its original position.

Question 2

What are transverse waves?

Answer 2

Waves produced when oscillations or vibrations are perpendicular to the direction of energy transfer.
Peaks and troughs form at points of maximum displacement.

Question 3

What are longitudinal waves?

Answer 3

Waves produced when oscillations are parallel to the direction of energy transfer. Compressions and rarefactions form.

When sound waves travel through air, air particles are displaced and bounce off their neighbours. These collisions provide the restoring force however particles don’t move along the wave.

Question 4

What’s displacement (of waves)?

Answer 4

Distance from equilibrium to a particular direction - a vector.

Question 5

What’s amplitude?

Answer 5

As displacement from equilibrium position.

Question 6

What’s wavelength?

Answer 6

Minimum distance between two points in phase of adjacent waves.

Question 7

What’s the period of oscillation?

Answer 7

The time taken for one oscillation or time for one wavelength to pass a certain point.

Question 8

What’s frequency?

Answer 8

The number of wavelengths passing a point per unit time.

Question 9

What’s wave speed?

Answer 9

The distance travelled by the wave per unit time.

Question 10

What is phase difference?

Answer 10

The difference between the displacement of particles along a wave, or the difference in displacements of particles in different waves, given in degrees or radians.
When phase difference is zero, the waves in in phase.
When phase difference is 180°, the waves are in anti phase.

Question 11

What’s reflection?

Answer 11

The change in direction of a wave at a boundary between media, remaining in the original medium.

Question 12

How are wavelength and frequency affected by reflection?

Answer 12

They don’t change.

Question 13

What’s the law of reflection?

Answer 13

Angle of incidence = angle of reflection

Question 14

What’s refraction?

Answer 14

The change in direction of a wave as it passes from one medium to another, changing speed.
There is always reflection when refraction occurs.

Question 15

How does refraction affect wavelength and frequency?

Answer 15

If the wave slows down, wavelength decreases and frequency remains the same.

If the wave speeds up, wavelength increases and frequency remains he same.

Question 16

What happens when a water wave enters a shallower region?

Answer 16

Due to refraction, it slows down and wavelength decreases / gets shorter.
Frequency however remains the same.

Question 17

What’s diffraction?

Answer 17

A property of waves where waves spread out as they pass a gap or obstacle.

Question 18

How does diffraction affect wavelength and frequency?

Answer 18

Speed, wavelength and frequency don’t change however the amount of diffraction is dependent upon the size of the gap.

Question 19

What is polarisation?

Answer 19

When particles oscillate in one direction only e.g. up and down, so the wave only travels in a single plane.

Un polarised sources e.g. unpolarised light has oscillations in all directions.
Longitudinal waves can’t be polarised as they’re already in one plane.

Question 20

What is partial polarisation?

Answer 20

When the majority of waves are oscillating in one plane however it’s not completely polarised e.g. When transverse waves are reflected off a surface.

Question 21

What is intensity (of a progressive wave)?

Answer 21

The radiant power passing through a ur face per unit area in watts per m2.
Radiant power of a wave from a source spreads out as a sphere. As distance / radius increases, intensity decreases.

Question 22

What is the intensity-distance inverse square relationship?

Answer 22

I = P/A

I = P / 4 * pi * r2

Question 23

How are intensity and amplitude related?

Answer 23

Intensity is directly proportional to amplitude squared.

Question 24

What is the range of wavelengths of electromagnetic waves?

Answer 24

10^6 (radio) to 10^-16 (gamma)

However the waves are categorised by their origin not wavelength

Question 25

How can unpolarised electromagnetic waves be polarised?

Answer 25

By using polarising filters which only allow waves of a certain orientation to pass through.

Question 26

What is refractive index, n?

Answer 26

A property of different materials which explains at what angle a wave would be refracted.

nSinØ = k

And

n1SinØ1 = n2SinØ2

Question 27

What is total internal reflection?

Answer 27

When all light is reflected back to the original medium and none is refracted.

Question 28

What are the 2 conditions required for total internal reflection?

Answer 28

The light must be travelling through a medium with a higher refractive index as it strikes the boundary of a medium with a lower refractive index.

The angle at which the light strikes the boundary must be above the critical angle which depends on the refractive index of the medium.

Question 29

What is superposition?

Answer 29

When two waves of the same type meet, overlap/superpose and pass through each other, producing a single wave.

Question 30

What’s the principe of superposition?

Answer 30

When two waves meet at a point, the resultant displacement at that point is equal to the sum of the displacements of the individual waves.

Question 31

What is interference?

Answer 31

The effect when two progressive waves interact to produce a resultant wave.
There can be constructive and destructive interference.

Question 32

What’s constructive and destructive interference?

Answer 32

Constructive - when two waves are in phase and their crests or troughs overlap to produce a resultant wave with a greater amplitude.

Destructive - when two waves are in anti phase as a crest aligns with a trough to produce a resultant wave with a smaller amplitude.

Question 33

What’s coherence?

Answer 33

Waves emitted from different sources which have a constant phase difference and same frequency.

Question 34

How are maxima and minima produced?

Answer 34

By interference.

Maxima are produced by constructive interference and minima form by destructive interference.

Question 35

What’s path difference?

Answer 35

The difference in distance between interfering points of coherent waves.

Question 36

What did Young’s double slit experiment prove?

Answer 36

That light has wave like features.
A monochromatic light was shone through a single narrow slit (to diffract the light) then through the double slits.
Each slit acts as a source of coherent waves, which spread and overlapped, forming bright and dark fringes.

Question 37

For the double slit formula “wavelength = ax/D”, what are ‘a’, ‘x’ and ‘D’?

Answer 37

a - the separation between slits

x - the separation between fringes

D - distance from the slits to the screen where the fringes form

The equation only works of a &laquo_space;D

Question 38

What is a stationary/standing wave?

Answer 38

A wave formed when 2 progressive waves with the same frequency and amplitude travel in opposite directions are superpose.

Question 39

What’s a node and anti node?

Answer 39

A node is where displacement within a stationary wave is zero due to the waves being in anti phase so amplitude is zero.

An anti node is where the waves are always in phase so amplitude is at it’s greatest.

The distance between a node and antinode is half a wavelength.

Question 40

What is the direction of energy transfer of stationary waves?

Answer 40

There’s no net energy transfer since the waves travel in opposite directions.

Question 41

What’s the fundamental frequency?

Answer 41

The minimum frequency of a stationary wave.

Question 42

How are stationary waves produced in a tube?

Answer 42

If one end is closed, one end must be a node and the other is an antinode. These fundamental frequencies will always be in an odd number.

If both ends are open, both ends must be antipodes. Fundamental frequencies can be of any number.

Question 43

What are the 2 main types of seismic waves?

Answer 43

P-waves (primary) and S-waves (secondary) which are both progressive waves.

P waves are longitudinal whereas S waves as transverse. They can be used to identify the thickness of layers of the Earth.

Question 44

Explain how the stationary wave is formed on a string.

Answer 44

The wave is reflected (at the fixed end of the wire) and interferes/superposes with the incident wave
This produces a resultant wave with nodes and antinodes where there is no energy transfer.

Question 45

What’s phase difference?

Answer 45

How far ‘out of step’ (out of sync) the oscillations at two points on the wave/string are.