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Physics > Module 4.4 - Waves > Flashcards

Module 4.4 - Waves Flashcards

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1
Q

Define progressive wave

A

A wave that transfers energy away from a source

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2
Q

Define wavelength

A

The smallest distance between one point on a wave and the identical point on the next wave

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3
Q

Define period

A

Time taken for one complete pattern of oscillation

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4
Q

Define frequency

A

The number of oscillations per unit time

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5
Q

Define displacement

A

The distance travelled in a particular direction by a wave from its mean or rest position

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6
Q

Define amplitude

A

The maximum displacement of a wave from its mean or rest position

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7
Q

Define phase difference

A

The difference (in radians) in the phases of two waves of the same frequency

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8
Q

Define path difference

A

The difference (in metres) between the distances travelled by two waves arriving at the same point, in relation to the wavelength

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9
Q

Define intensity

A

The rate at which energy is transferred from one location to another as the wave travels through space, perpendicular to the direction of wave travel

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10
Q

Define reflection

A

When waves rebound from a barrier, changing direction but remaining in the same medium

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11
Q

Define refraction

A

When waves change direction when they travel from one medium to another due to a difference in the wave speed in each medium

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12
Q

Define diffraction

A

When a wave spreads out after passing around an obstacle or through a gap

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13
Q

Define interference

A

The addition of two or more waves that results in a new wave pattern due to the principle of superposition

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14
Q

Define electromagnetic wave

A

A self-propagating transverse wave that does not require a medium to travel through

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15
Q

Define polarisation

A

The process of turning an unpolarised wave into a plane-polarised wave

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16
Q

Define plane-polarised wave

A

A transverse wave oscillating in only one plane

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17
Q

Define polarising filter

A

Produces a plane-polarised wave of light by selective absorption of one component of the incident oscillations
The filter transmits only the component of light polarised perpendicular to that direction

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18
Q

Define refractive index

A

A value that indicates how quickly or slowly EM radiation will travel through a medium

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19
Q

Define total internal reflection

A

When EM radiation travels from a material of a higher refractive index to one of a lower refractive index and the angle of incidence is larger than the critical angle

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20
Q

Define critical angle

A

The angle of incidence when the angle of refraction is 90°

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21
Q

What is the principle of superposition?

A

It states that when two or more waves of the same type meet, the resultant wave can be found by adding the displacements of the individual waves

22
Q

Define constructive interference

A

Occurs when two waves meet in phase

23
Q

Define destructive interference

A

Occurs when two waves arrive at a point out of phase

24
Q

Define coherent

A

Two waves with a constant phase relationship

25
Q

Define diffraction grating

A

A piece of optical equipment made from glass, onto which many thousands of very thin, parallel and equally spaced grooves have been accurate,y engraved using a diamond

26
Q

Define order

A

The number of the pattern (n) on either side of the central maximum

27
Q

How to calculate period from an oscilloscope

A

Distance between peaks x time base setting

28
Q

What does it mean if two waves are in phase?

A

Exact same pattern of oscillation

No phase difference

29
Q

What does it mean if two waves are in antiphase?

A

Exact opposite pattern of oscillation

Half a cycle phase difference

30
Q

How to covert from degrees to radians

A

Divide by 180

Multiply by pi

31
Q

How to convert from radians to degrees

A

Multiply by 180

Divide by pi

32
Q

How to derive the wave equation

A

Speed = distance / time
In one period, T, wave travels one wavelength: v = wavelength / T
F = 1 / T, so substitute f for 1 / T
V = wavelength x frequency

33
Q

Why is intensity proportional to the amplitude squared?

A

The amplitude of a wave decreases as the wave spreads out from a source
Energy of a wave is proportional to the amplitude squared
Therefore intensity is also proportional to the amplitude because intensity relates to energy transfer

34
Q

When is diffraction shown the most clearly?

A

Wavelength of diffracted wave is equal to gap that it is travelling through

35
Q

Law of reflection

A

Angle of incidence = angle of reflection

36
Q

Snell’s Law

A

n1 x (sin x incident angle) = n2 x (sin x refracted angle)

37
Q

Formula for critical angle

A

sin x critical angle = n2 / n1
n1 = refractive index of more dense medium
n2 = refractive index of less dense medium

38
Q

What happens when the angle of incidence is less than the critical angle?

A

The ray is refracted with very little reflection

39
Q

What happens if the angle of incidence is equal to the critical angle?

A

The ray emerges along the edge of the block

40
Q

What happens if the angle of incidence is greater than the critical angle?

A

The ray is totally internally reflected

41
Q

Conditions for total internal reflection

A

Angle of incidence must be greater than the critical angle

Incident substance must have larger refractive index

42
Q

Applications of total internal reflection

A

Fibre optics to send information (often telephone calls or internet access) at the speed of light through a fibre optic
Quicker and can carry more information

43
Q

Diffraction if the gap is smaller than the wavelength?

A

No diffraction

Waves are reflected by barrier

44
Q

Diffraction if width of gap is similar to wavelength?

A

Diffraction occurs

45
Q

Diffraction if width of gap is equal to wavelength?

A

Maximum diffraction

46
Q

Diffraction if width of gap is larger than wavelength?

A

Slight diffraction at waves’ edges

47
Q

Similarities between progressive and stationary waves

A

Neither transfers matter

Both can be longitudinal or transverse

48
Q

Differences between progressive and stationary waves

A

Progressive transfers energy in direction of propagation - for stationary there is no transfer of energy
For progressive, all points are out of phase along one wavelength (e.g. crest and trough by 180°) - for stationary, points between 2 nodes or an even number of nodes are in phase, points between an odd number of nodes are in antiphase
For progressive, all particles have the same amplitude - for stationary, amplitude varies according to position (0 at nodes)

49
Q

What does the frequency of the vibrations on a string depend on?

A

Mass per unit length
Tension
Length of the string

50
Q

Define the fundamental mode of vibration

A

The length of the string is half the wavelength, producing the lowest possible frequency (first harmonic)

51
Q

Define harmonics

A

Whole number multiples of the fundamental frequency of a stationary wave

52
Q

Describe an experiment to determine the speed of sound in air

A

Use a tuning fork of a known frequency and a tube of water held by a clamp so its length can be altered
When the tuning fork is struck above the tube of water, a stationary wave will be set up in the tube
The fundamental frequency can be obtained by listening carefully and finding the minimum length at which the sound is loudest (when the length of the tube is equal to a quarter of the wavelength)
Lengthen the tube and the sound will decrease in volume before reaching its second maximum loudness
The difference between these two lengths is half a wavelength, so multiply by 2 to find the speed of sound in air

Physics (19 decks)

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