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PHYSICS A LEVEL REVISION - LVI > Waves > Flashcards

Waves Flashcards

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1
Q

State Malus’ law.

A

I2 = I1 cos^2 (theta)

If the amplitude of the light passing through the second vector is E2 = E1 cos (theta)

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2
Q

Define wavelength.

A

The distance between two successive points on a wave that are in phase

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3
Q

What is a longitudinal wave?

A

Progressive waves whose displacements are parallel to the direction of energy flow. They require a medium and include compressions and rarefactions

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4
Q

What is phase difference and what is it measured in?

A

How much a particle/wave lags behind another particle/wave. Measured in radians, degrees or fractions of a cycle

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5
Q

How can you find out the time period of a wave using its frequency?

A

Time period = 1/frequency

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6
Q

Define amplitude.

A

The maximum displacement of the wave from its equilibrium position

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7
Q

Define frequency and give its units.

A

The number of waves passing a point per second, measured in hertz, Hz

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8
Q

What is the Principle of Superposition?

A

When two or more waves meet, the resultant displacement of the medium is the algebraic sum of the individual displacements

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9
Q

Other than electromagnetic radiation, give two examples of transverse waves.

A

Secondary ‘s’ waves

Water waves in a ripple tank

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10
Q

State two differences between a transverse waves and longitudinal waves.

A

In transverse waves the oscillation of the medium is perpendicular to the direction of wave travel

Transverse waves can be polarised

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11
Q

State one application of a polarising filter and a reason for its use.

A

Polaroid sunglasses - to reduce glare from a windscreen

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12
Q

The sound quality of a radio is improved by adjusting the orientation of the aerial. Why?

A

The radio waves from the transmitter are polarised so to improve the sound quality, the aerial should be aligned in the same plane of polarisation as the radio waves

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13
Q

By approximately how many times is the wavelength of audible sound waves greater than the wavelength of light waves?

A

10^6 times greater

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14
Q

What property of light waves do polarising sunglasses depend on?

A

Light waves may be polarised when reflected from a surface

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15
Q

Which wave has the greater frequency: light waves or sound waves?

A

Light waves have far greater frequencies than sound waves

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16
Q

Which wave has the greater wavelength: light waves or sound waves?

A

Sound waves have far greater wavelengths than light waves

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17
Q

Describe what an observer would see when a second polarising filter is rotated through 360º.

A

Variation in light intensity between maximum and minimum in 360º rotation

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18
Q

Why is it important to correctly align the aerial of a TV in order to receive the strongest signal?

A

Transmitted radio waves are often polarised to the aerial must be aligned in the same plane of polarisation

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19
Q

Describe the motion of a particle in a transverse wave.

A

It would oscillate perpendicular to the direction of energy transfer, from equilibrium to a maximum displacement, back to equilibrium then to a minimum displacement and back to equilibrium

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20
Q

Which of the following waves cannot be polarised?

a. radio
b. ultrasonic
c. microwave
d. ultraviolet

A

Ultrasonic as it is a longitudinal wave

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21
Q

State the characteristic features of longitudinal waves.

A

Particles oscillate parallel to the direction of energy transfer, in rarefactions and compressions

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22
Q

State the characteristic features of transverse waves.

A

Particles oscillate perpendicular to the direction of energy transfer, in peaks and troughs

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23
Q

What is the equation for wave speed?

A 
c = f x (lamda)
v = f x (lamda)
24
Q

What is detected by a microwave detector when it reaches a maxima of intensity?

A

Maxima are antinodes - two waves interfere constructively giving large amplitude and much energy is stored there

25
Q

What is detected by a microwave detector when it reaches a minima of intensity?

A

Minima are nodes - two waves interfere destructively and cancel out so amplitude equals 0 and no energy is stored there

26
Q

Give 5 key features of a stationary waves.

A
  • 2 progressive waves
  • travelling in opposite directions/reflected
  • same amplitude
  • same frequency
  • overlap and obey laws of superposition
27
Q

How would you calculate the frequency of an overtone?

A

f4 = f1 x 4

Frequency of overtone = fundamental mode times the number of loops

28
Q

A stationary wave is set up on a string with length l, and diameter d.

Another wave is set up on another string with equal tension and same material. What l and d are needed for the same fundamental frequency as the first string?

A

l/2, 2d

As f, (rho), T and 4 are constants, and L x D = constant

29
Q

The frequency of the first harmonic is f. The length and tension are doubled, what is f now?

A

f / (square root of 2)

30
Q

Why could actual frequencies on a stretched string be different to predictions

A

Diameter of the string may be reduced as it is stretches, giving a lower mass per unit length and therefore a higher frequency than anticipated

31
Q

What is the equation for wavelength using time period, T?

A

(lamda) = v / (1/T)

32
Q

What is the equation for phase difference?

A

phase difference = (2 pi x path difference) / (lamda)

2 pi can be exchanged for 360 if answer wanted in degrees

33
Q

What is the degree equivalent of phase difference pi/3 radians?

A

pi / 3 = 60º = 1/6 of a wavelength

34
Q

What is the degree equivalent of phase difference 2 pi/5 radians?

A

2 pi / 5 = 72º = 1/5 of a wavelength

35
Q

What is the degree equivalent of phase difference 2 pi/3 radians?

A

2 pi / 3 = 120º = 1/3 of a wavelength

36
Q

What are the two types of seismic waves, and what type of wave is each?

A

Primary waves are longitudinal, secondary waves are transverse

37
Q

Define a transverse wave.

A

Progressive waves whose displacements are perpendicular to the direction of energy transfer. They do not require a medium and contain crests and peaks

38
Q

Describe the motion of a particle on a transverse wave over one complete time period.

A

The particle oscillates about the equilibrium position vertically upwards to a maximum positive displacement, down to a maximum negative displacement, and up to the equilibrium position

39
Q

Describe the relationship between the magnetic field variation and the electric field variation.

A

They are perpendicular to each other

40
Q

When discussing the plane of vibration, which field are we looking at and why?

A

The electric field as the electric field causes the magnetic field

41
Q

What are the four ways of producing plane polarised light?

A

Transmission (main), Reflection, Refraction, Scattering

42
Q

Outline how cellophane produces plane polarised light.

A

It is an optically active material that rotates the plane of polarised light. The angle of rotation is dependent on thickness and wavelength

43
Q

Give an example of light that is plane polarised due to reflection.

A

Water on the ground reflects light which is horizontally plane polarised

44
Q

How can a camera use polarisation?

A

The polarising filter reduces reflected, plane polarised light, making it easier to take photographs through glass

45
Q

How can calcite crystals produce plane polarised light?

A

They exhibit double refraction, splitting the light into two plane polarised rays that are mutually perpendicular, termed ordinary and extraordinary

46
Q

How can some signals be detected from a microwave source with a filter at 45º to the horizontal?

A

The microwave can be split into two components, one of which is absorbed by the filter and the other passes through the filter

47
Q

How is a sonic boom formed?

A

As an object travels faster than the speed of sound, the sound waves it produces overlap, forming a Mach cone. When the object has passed, the observer will hear a sonic boom

48
Q

What is the approximate wavelength of radio waves?

A

10^3 - 10^1 metres

49
Q

What is the approximate wavelength of microwaves?

A

10^-2 metres

50
Q

What is the approximate wavelength of infrared radiation?

A

10^-4 metres

51
Q

What is the approximate wavelength of visible light?

A

10^-6 metres

52
Q

What is the approximate wavelength of ultraviolet light?

A

10^-8 metres

53
Q

What is the approximate wavelength of x-rays?

A

10^-10 metres

54
Q

What is the approximate wavelength of gamma rays?

A

10^-12 metres

55
Q

Define constructive interference.

A

Two or more waves meeting at a point enhance one another at all times.

56
Q

Define destructive interference.

A

Two or more waves meeting at a point oppose one another at all times and have zero resultant

PHYSICS A LEVEL REVISION - LVI (9 decks)

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