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Physics Unit 2 (AQA) > Waves > Flashcards

Waves Flashcards

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1
Q

Define a Transverse wave

A

A wave in which the direction of vibration is perpendicular to the direction in which the wave travels.

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2
Q

State the condition required for a transverse wave to be polarised

A

It’s vibrations must stay in one plane only

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3
Q

Explain how longitudinal waves become polarised

A

They can’t

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4
Q

Define the plane of polarisation of an electromagnetic wave

A

The plane in which the electric field oscillates

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5
Q

Define a longitudinal wave

A

A wave in which the direction of vibration of the particles is parallel to the direction in which the wave travels

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6
Q

Define the displacement of a wave

A

A particles distance and direction from its equilibrium position

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7
Q

State an equation to calculate speed (c) given f

A

C = fλ

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8
Q

Define the phase difference of 2 vibrating particles

A

The fraction of a cycle between the vibrations of the two particles
Where 1 cycle = 360° = 2π

∴ phase difference (in radians) = 2πd / λ
(Where d = distance along the wave)

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9
Q

State the principle of superposition

A

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

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10
Q

What is the distance between adjacent nodes in a stationary wave?

A

λ/2

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11
Q

State the 3 conditions required for the formation of a standing wave

A

1) 2 waves travelling towards each other
2) Same frequencies
3) Superpose

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12
Q

On a standing wave, what are the names given to:

i) points of no amplitude
ii) points of maximum amplitude

A

i) nodes

ii) antinodes

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13
Q

State a difference between energy transfer of a progressive wave and a stationary wave

A

Stationary waves do not transfer energy

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14
Q

Describe the phase of all the particles between adjacent nodes

A

They are all in phase

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15
Q

Describe the phase of the particles either side of a node

A

They are out of phase

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16
Q

Define electromagnetic waves

A

Vibrating electric and magnetic fields that progress through space without need for a substance
The vibrating electric field creates a vibrating magnetic field, which generates a vibrating electric field further away, and so on

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17
Q

State the types of electromagnetic waves in order of lowest to highest frequency

A
  • Radiowaves
  • Microwaves
  • Infra Red
  • Visible Light
  • Ultra Violet
  • X-Ray
  • Gamma Ray
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18
Q

Define amplitude

A

The maximum displacement of a vibrating particle

For a transverse wave it is the height of a wave crest or the depth of a wave trough from the middle

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19
Q

Define wavelength

A

The least distance between two adjacent vibrating particles with the same displacement and velocity at the same time (e.g. distance between adjacent crests)

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20
Q

Define complete cycle

A

From the maximum displacement to the next maximum displacement (e.g. from one wave peak to the next)

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21
Q

Define wave period (Time period)

A

The time for one complete wave to pass a fixed point

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22
Q

Define frequency and give its units

A

The number of cycles of vibration of a particle per second, or the number of complete waves passing a point per second
Units: Herts (Hz)

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23
Q

Give the equation for the time period of a wave

A

T = 1 / f

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24
Q

State and describe the set up of a piece of apparatus to view the interference of light by waves

A

A ripple tank
An electronic ‘dipper’ is set up just above a shallow, transparent tank of water with sloping sides. A stroboscope is used in accordance with a lamp so that the wavefronts are projected onto a surface below

25
Q

State the significance of the sloped sides of a ripple tank

A

It prevents the waves from reflecting off the sides of the tank, which would make it more difficult to see the wavefronts projected.

26
Q

Describe the reflection of a straight wave on a hard flat surface

A

Straight waves directed at a certain angle to a hard flat surface reflect off at the same angle.
Therefore, the direction of the reflected wave is at the same angle to the reflector as the direction of the incident wave

27
Q

Define refraction

A

When waves pass across a boundary at which the wave speed changes, the wavelength also changes
If the wavefronts are at a non-zero angle to the boundary, they change direction as well as speed

28
Q

State when the refraction of light is observed

A

Refraction of light is observed when a light ray is directed into a glass block non-normally
The light ray changes direction when it crosses the glass boundary because light waves travel more slowly in glass than in air

29
Q

Define diffraction

A

Diffraction occurs when waves spread out after passing through a gap or round an obstacle

30
Q

State when diffraction is observed in water

A

When straight waves in a ripple tank are directed at a gap

31
Q

What 2 factors affect the amount of diffraction for waves passing through a gap

A
  • The narrower the gap, the more the waves spread out

- The longer the wavelength. the more the waves spread out

32
Q

In which direction do satellite dishes in Europe need to point and why?

A

South, because the satellites orbit the Earth directly above the equator

33
Q

Explain the significance of the size of a satellite dish on the signal it receives

A

The larger the satellite dish, the stronger the signal it can receive, because more radiowaves are reflected by the dish onto the aerial.

34
Q

Define superposition

A

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

35
Q

Where waves interact, what happens when:

i) A crest meets a crest?
ii) A trough meets a trough?
iii) A crest meets a trough?

A

i) A supercrest is created
ii) A supertrough is created
iii) The resultant displacement is 0; the two waves cancel each other out

36
Q

Give 2 examples of superposition

A

1) Stationary waves on a rope

2) Water waves in a ripple tank

37
Q

What must the 2 sources of waves be to produce a interference between the 2 waves and why is this effect shown?

A

Coherent
An interference pattern where they overlap is produced, because they vibrate at the same frequency with a constant phase difference

38
Q

Describe an experiment to demonstrate the reflection, refraction, interference and polarisation of microwaves

A

The transmitter produces microwaves of wavelength 3.0cm. The reciever can be connected to a suitable meter, which gives a measure of the intensity of microwaves at the reciever

1) Place the receiver in the path of the microwave beam from the transmitter. As you move it further away from the transmitter the signal decreases, showing that microwaves become weaker at further distances from the transmitter
2) Place a metal plate between the transmitter and receiver to show that microwaves cannot pass through metal
3) Use 2 metal plates to make a narrow slit and show that the receiver detects microwaves that have been diffracted as they pass through the slit. Show that if the slit is wider, less diffraction occurs
4) Use a narrow metal plate with 2 plates either side to make a pair of slits. Direct the transmitter at the slits and use the receiver to find points of cancellation and reinforcement, where the microwaves from the 2 slits overlap

39
Q

Describe how stationary waves are formed

A

A stationary wave is formed when 2 progressive waves pass through each other.
This can be achieved on a string in tension by fixing both ends and making the middle part vibrate, so progressive waves travel towards each end, reflect at the ends and then pass through each other

40
Q

Define a node

A

A fixed point of no displacement

41
Q

State the distance between adjacent nodes

A

Distance between adjacent nodes = ½λ

42
Q

Define antinode

A

The point midway between 2 adjacent nodes which has maximum amplitude

43
Q

Define fundamental mode of vibration

A

The simplest stationary wave pattern on a string, consisting of a single loop that has a node at either end

44
Q

Describe the energy transfer for stationary waves vibrating freely

A

They do not transfer energy because the nodes and antinodes are at fixed positions

45
Q

Describe stationary waves in terms of the progressive waves that cause them

A

Considering the 2 progressive waves passing through each other:

  • When they are in phase, they reinforce each other to produce a large wave
  • A quarter of a cycle later, the 2 waves have each moved one-quarter of a wavelength in opposite directions, thus are now in antiphase, so cancel each other out
  • After a further quarter cycle, the 2 waves are back in phase. The resultant is again a large wave except reversed
46
Q

For 2 vibrating particles in a stationary wave, describe:

i) The amplitude
ii) The phase difference

A

i) The amplitude of a vibrating particle varies with position from 0 (at a node) to maximum (at an antinode)
ii) The phase difference between 2 vibrating particles is:
- 0 if the two particles are between adjacent nodes or separated by an even number of nodes
- 180° (= λ radians) if the 2 particles are separated by an odd number of nodes

47
Q

Give the similarities between the frequency of stationary and progressive waves

A

Stationary: All particles except at the nodes vibrate at the same frequency
Progressive: All particle vibrate at the same frequency

48
Q

Give the differences between the amplitude of particles of stationary and progressive waves

A

Stationary: The amplitude varies from 0 (at the nodes) to a maximum (at the antinodes)
Progressive: All particles have the sane amplitude

49
Q

Describe the phase difference between 2 particles for stationary and progressive waves

A

Stationary: Equal to mπ, where m is the number of nodes between the two particles
Progressive: Equal to 2πd/λ, where d is the distance apart and λ is the wavelength

50
Q

State the resonant frequency for the standing waves in an air-filled pipe closed at one end

A

In a pipe closed at one end, the resonant frequencies occur when there is an antinode at the open end and a node at the other end

51
Q

Describe how standing waves can be detected using microwaves

A

A microwave transmitter is directed at a metal plate which reflects them back towards the transmitter.
When a detector is moved along the line between the transmitter and the metal plate, the detector signal is found to be 0 at equally spaced positions (half wavelengths apart) because the reflected waves interfere with the waves from the transmitter and form a stationary wave pattern

52
Q

Define fundamental pattern of vibration

A

The lowest possible frequency produced by a vibrating system. Has an antinode at the middle as well as a node at either end.
Because the length L of the vibrating section of the string is between adjacent nodes and the distance between adjacent nodes is ½λ - the wavelength of the waves that form this pattern, the fundamental wavelength is:
λ₀ = 2L

53
Q

Give the equation for the fundamental frequency from the fundamental wavelength

A

λ₀ = 2L
f₀ = c / λ₀ = c / 2L
where c is the speed of the progressive waves on the wire

54
Q

Define first overtone

A

The next stationary wave pattern from the fundamental pattern of vibration, where there is a node at the middle, so the string is in 2 loops
Therefore the waves that form this pattern:
λ₁ = L
Because each loop has a length of half-a-wavelength

55
Q

Give the equation for the frequency of the first overtone, and its relation to the fundamental frequency

A 
λ₁ = L
f₁ = c / λ₁ = c / L = 2f₀
56
Q

Define second overtone

A

The next stationary wave pattern from the fundamental pattern of vibration, where there is an antinode in the middle and the nodes are distance ⅓L from each other
The wavelength of waves that form this pattern are:
λ₂ = ⅔L

57
Q

State the condition for the formation of a stationary wave in terms of the time take for a wave to travel along the sting and back

A

The time taken for a wave to travel along the string and back must be equal to the time taken for a whole number of cycles of the vibrator
f = mc /2L = mf₀
where m is a whole number

58
Q

For a string, how would you:

i) raise the pitch?
ii) lower the pitch?

A

i) Increasing the tension or shortening the length

ii) Decreasing the tension or increasing the length

Physics Unit 2 (AQA) (7 decks)

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