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Physics Michael > P1.5 Waves > Flashcards

P1.5 Waves Flashcards

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1
Q

What is a wave?

A

A vibration that transfers energy without transferring any matter

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2
Q

How do waves transfer energy?

A

By making the particles that it is travelling through vibrate

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3
Q

What does a wave on axes show?

A

The displacement of one particle from its rest position as the wave moves over time/distance

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4
Q

What do crests and troughs show on a displacement wave graph?

A

They are the peaks of the wave, the crests show the maximum displacement from the particle’s rest position and the troughs show the minimum displacement

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5
Q

What is the amplitude of a wave?

A

The displacement from the rest position to a crest or a trough

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6
Q

What is the wavelength of a wave?

A

The length of a full cycle of the wave e.g. the distance from crest to crest

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7
Q

What is the frequency of a wave?

A

The number of complete waves passing a certain point per second or the number of waves produced by a source per second

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8
Q

What is frequency measured in?

A

In hertz (Hz), 1 Hz is 1 wave per second

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9
Q

What is the equation for the speed of a wave?

A

v = f x λ // Speed in m/s = frequency in Hz x wavelength in m

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10
Q

In what direction do waves transfer energy?

A

In the same direction as they travel

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11
Q

What is a transverse wave?

A

Waves which have vibrations that are perpendicular (90°) to the direction of energy transfer of the wave

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12
Q

What are three examples of transverse waves?

A

Light and all other electromagnetic waves, ripples on water and waves on strings

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13
Q

What are areas of compression in a longitudinal wave?

A

Where particles are bunched together

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14
Q

What are areas of rarefaction in a longitudinal wave?

A

Where particles are spread out

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15
Q

What is a longitudinal wave?

A

A wave that has vibrations that are parallel to the direction of energy transfer of the wave

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16
Q

What are three examples of longitudinal waves?

A

Sound waves, ultrasounds and some earthquake waves called seismic waves

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17
Q

What do mechanical waves need in order to travel?

A

They need a medium to travel in - they can’t travel in a vacuum

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18
Q

Are mechanical waves transverse or longitudinal waves?

A

They can be either

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19
Q

What are examples of mechanical waves? (3)

A

Water waves, sound waves and waves in springs

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20
Q

How can waves change their direction of travel when they arrive at an obstacle or meet a boundary? (3)

A

By reflection, refraction or diffraction

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21
Q

What is reflection?

A

When a wave meets a boundary between two media it can bounce back (it took an L, lol xD ROFL)

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22
Q

What does reflection allow humans to do?

A

It allows us to see objects - the reflection of light bounces of objects and into our eyes

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23
Q

What happens when light is reflected form a smooth, even surface?

A

The light is reflected at the same angle and you get a clear reflection

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24
Q

What happens when light is reflected from an uneven surface?

A

The light is reflected off at different angles

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25
Q

What is refraction?

A

When a wave changes direction as it crosses a boundary between media

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26
Q

What is the ‘normal’ of a boundary?

A

An imaginary line that’s perpendicular (90°) to the boundary at the point of incidence (where the wave hits the boundary)

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27
Q

How do waves need to meet the boundary in order to be refracted?

A

Waves are only refracted if they meet the boundary at an angle to the normal - waves travelling along the normal are not refracted

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28
Q

What is diffraction?

A

When waves spread out at

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29
Q

When do waves diffract?

A

At the edges when they pass through a gap or pass an obstacle

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30
Q

What does the amount of diffraction depend on?

A

The size of the gap relative to the wavelength of the wave - the narrower the gap, or the longer the wavelength, the more the wave spreads out

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31
Q

Why does sound need a large gap to diffract?

A

Because it has a long wavelength

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32
Q

Why does light need a small gap to diffract?

A

Because it has a short wavelength

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33
Q

What are electromagnetic waves a group of?

A

Transverse waves

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34
Q

What is the electromagnetic spectrum?

A

A continuous spectrum of all possible wavelengths of electromagnetic waves

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35
Q

What happens when you go from left to right in the EM spectrum? (2)

A

Frequency and energy increase

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36
Q

What happens when you go from right to left in the EM spectrum?

A

Wavelength increases

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37
Q

What important things are there to know about EM waves? (3)

A

They vary in wavelength from around 10⁻¹⁵m to 10⁴m, they all travel at the same speed 3 x 10⁸m/s in a vacuum, and EM waves with higher frequencies have shorter wavelengths

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38
Q

Radio waves are an example of an EM wave, what are they used for? (2)

A

For radio and TV signals

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39
Q

What happens when a long radio wave comes into contact with the curvature of the earth?

A

Long-wave radio can be transmitted and received halfway round the world because the wavelengths diffract (bend) around the curved surface of the earth

40
Q

What allows long-wave radio to be received from somewhere which isn’t in line of sight of the transmitter?

A

Long radio waves can diffract around hills, into tunnels and much more - this allows the radio waves to reach receivers which aren’t in the line of sight of the transmitter

41
Q

Short-wave radio signals don’t diffract around the earth but can still be received at large distances, why?

A

Because they reflect between the earth and the ionosphere (this is similar for medium-length signals, but they depend on the atmospheric conditions and the time of day)

42
Q

What is the ionosphere?

A

An electrically charged layer in the Earth’s upper atmosphere

43
Q

What waves do TV and FM radio transmit? How does this affect you as a viewer?

A

They have very short-wave radio signals - which means you need to be in direct sight of transmitter to get reception

44
Q

Why are microwaves used for communication to and from satellites?

A

Because some microwaves can easily pass through the Earth’s atmosphere without being reflected, refracted, diffracted or absorbed - so they can reach satellites

45
Q

What happens when a microwave reaches a satellite?

A

Once the satellite has received the signal, it transmits the signal back to earth but in a different direction where it’s received by a satellite dish on the ground

46
Q

How do mobile phones use microwaves?

A

They use microwaves to send signals between your phone and the nearest transmitter

47
Q

What are remote-sensing satellites used for? And how do they carry out this particular function?

A

They use microwaves to monitor the Earth from space - they can be used to ‘see’ through the clouds and monitor oil spill, track the movement of icebergs etc.

48
Q

What health concerns are there with using microwaves?

A

Some wavelengths of microwaves are absorbed by water molecules and heat them up - water molecules are in cells in human bodies which, when heated, can lead to cancer

49
Q

What are infrared waves used in? (2)

A

Remote controls and signals in optical fibres

50
Q

How do wireless remote controls use infrared waves to send commands to an appliance?

A

They emit different patterns of infrared waves to send different commands to an appliance e.g. a TV

51
Q

What are optical fibres?

A

Very thin wires with a glass or plastic core that can be used to transmit signals of infrared or visible light

52
Q

How are signals carried in optical fibres?

A

They are carried as pulses of light or infrared radiation and is reflected off the sides of a very narrow core from one end of the fibre to the other

53
Q

Why are optical fibres used in phone lines?

A

Because they can carry data over long distances very quickly

54
Q

What is infrared radiation also known as?

A

Heat radiation

55
Q

What gives out infrared waves?

A

All hot objects - the hotter the object the more infrared waves it gives out

56
Q

What can infrared radiation be used for in cameras?

A

They can be used to monitor temperatures - infrared cameras can create an image showing temperature variations and the images can be colour coded to show different amount of IR

57
Q

How do cameras use a lens?

A

The lens in a camera is used to focus visible light onto a light-sensitive film or electronic sensor

58
Q

What does the lens aperture control?

A

It controls how much light enters the camera

59
Q

What does the shutter speed in a camera determine?

A

How long the film or sensor is exposed to the light

60
Q

What does varying the aperture and shutter speed of a camera allow a photographer do?

A

It allows them to capture as much or as little light as they want in their photograph

61
Q

How do you draw the normal when drawing a simple reflection from a boundary?

A

The normal - which is perpendicular to the boundary at the point the incidence wave hits (it is also drawn as a dashed line)

62
Q

What is the angle of incidence?

A

The angle between the path of the incident wave and the normal

63
Q

What is the angle of reflection?

A

The angle between the path of the reflected wave and the normal

64
Q

What is the law of reflection?

A

Angle of incidence = angle of reflection

65
Q

What is an image?

A

A picture of an object formed by light from the object

66
Q

What is a virtual image?

A

An image that is formed when light rays appear to appear to have come from a point that they don’t actually pass through

67
Q

What happens when you put up a screen where a virtual image appears to meet?

A

The image will not appear on the screen, because the light rays forming it aren’t actually there

68
Q

What does a virtual image look like?

A

Upright and laterally inverted

69
Q

What is a ray diagram?

A

A diagram that shows how the rays of light from an object form an image when reflected (or refracted)

70
Q

What are sound waves?

A

Mechanical vibrations (so they travel through the surrounding medium) caused by vibrating objects

71
Q

What type of wave are sound waves?

A

They are a type of longitudinal wave which move as a series of compressions

72
Q

How do people hear sound?

A

When the sound waves travel through someone’s ear and reach their eardrum

73
Q

From slowest to fastest, what do sound waves move fastest though?

A

Gas, liquid and solid

74
Q

Why can’t sound travel in space?

A

Because it’s mostly a vacuum so there are no particles to vibrateW

75
Q

What is an echo?

A

When sound waves reflect off of a hard flat surface, there is a delay between the original sound and the reflect sound waves because they have to travel further thus taking longer to reach the ear

76
Q

What happens when sound waves enter different media? e.g. from air to water

A

They refract (change direction)

77
Q

What does the pitch of a sound depend on?

A

The frequency of the sound wave - high frequency sound waves are high pitched, and low frequency sound waves are low pitch

78
Q

What does the loudness of a sound depend on?

A

The amplitude - the bigger the amplitude, the louder the sound

79
Q

What is the Doppler effect?

A

When you move towards or away from something that emits waves, the wavelengths and frequencies of the waves seem different

80
Q

What happens to the frequency and wavelength as you move towards a wave source?

A

The frequency will seem higher and the wavelength shorter

81
Q

What happens to the frequency and wavelength as you move away from a wave source?

A

The frequency will seem lower and the wavelengths longer

82
Q

What waves does the Doppler effect affect?

A

Both longitudinal and transverse waves

83
Q

What is the Doppler effect of a light source known as?

A

Red-shift

84
Q

What happens to a light source as it moves away from us?

A

The frequency of the light gets lower and shifts towards the red end of the spectrum - making the light appear redder than it actually is

85
Q

What happens to a light source as it moves away from us?

A

The frequency of the light gets higher and shifts towards the blue end of the visible light spectrum - making the light source appear bluer than it actually is, this is known as blue-shift

86
Q

What is shown on the absorption spectra?

A

A spectrum which shows what frequency of light each element absorb - a spectrum with dark lines in it is called a line absorption spectrum

87
Q

What do we see when comparing the absorption spectra of Earth and the absorption spectra from a distant galaxy?

A

We see the elements absorbing light waves with lower frequencies than they should be - they have shifted towards the red end of the spectrum (red shift)

88
Q

What does the red shift of galaxies show?

A

That they are moving away from us very quickly

89
Q

How does the red-shift of galaxies change compared to their distance from earth?

A

The further the galaxy, the more red-shift and the faster they are moving away from us

90
Q

What theory explains why distant galaxies are moving away from us?

A

Scientists believe a big explosion would have caused these galaxies to originally begin to move - the Big Bang theory

91
Q

What does the Big Bang theory state?

A

That all matter and energy in the universe was once compressed into a very small space - which then exploded, and the universe has been expanding ever since

92
Q

How can we estimate the age of the universe?

A

By using the current rate of expansion

93
Q

What is another theory of how the universe began?

A

The Steady State theory

94
Q

What is cosmic microwave background radiation (CMBR)?

A

Low-frequency electromagnetic radiation coming from all over the universe have been discovered, this is mostly found in the form of microwaves (CMBR)

95
Q

Why is the Big Bang theory greatly accepted?

A

Because it explains CMBR

96
Q

How does the Big Bang theory explain CMBR?

A

Just after the Big Bang the universe was extremely hot, and everything was emitting very high frequency radiation - but as the universe expanded, it has and this radiation has dropped in frequency and is now found as microwaves

97
Q

What problems are there with the Big Bang theory? (2)

A

It doesn’t explain how the explosion started in the first place and it doesn’t explain the what conditions were like pre-explosion

Physics Michael (14 decks)

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