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la física > Waves P2 > Flashcards

Waves P2 Flashcards

1
Q

What do waves transfer?

A

Energy from one place to another but no matter

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2
Q

What happens to particles when a wave travels through a medium?

A

Particles of a medium oscillate and transfer energy between each other but overall the particles stay in the same place because only energy is transferred

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3
Q

Identify the 2 types of wave

A

Longitudinal, transverse

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4
Q

What is the particle motion of a transverse wave like?

A

Particle motion/oscillations are perpendicular to the direction of energy movement

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5
Q

What is the particle motion of a longitudinal wave like?

A

Particle motion/oscillations are parallel to the direction of energy movement

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6
Q

Identify 4 transverse waves

A

Electromagnetic waves e.g light, ultraviolet, water, s-waves (secondary)

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7
Q

Identify 3 longitudinal waves

A

Sound, ultrasound, shock waves e.g p-waves (primary)

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8
Q

Define amplitude

A

Maximum displacement of a point on the wave from its undisturbed position (half height)

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9
Q

Define wavelength ( symbol is lambda)

A

The distance between same point on two adjacent waves (e.g trough to trough)

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10
Q

Define frequency

A

Number of complete waves passing a certain point per second. Measured in hertz (1Hz is 1 wave per second)

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11
Q

Define time period

A

Time for 1 complete cycle of a wave to pass a point

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12
Q

Equation for frequency

A

Number of waves divided by time (s)

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13
Q

Equation for velocity of waves

A

frequency x lambda

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14
Q

Equation for time period

A

1 divided by frequency

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15
Q

Define wave speed

A

The speed at which energy is being transferred

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16
Q

What is sound?

A

Vibrations that travel through a medium. These are longitudinal waves because air particles vibrate along the direction of travel of the wave

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17
Q

Why can’t you hear anything in space?

A

Space is a vacuum (empty) because the air particles are so far apart that there is no medium which longitudinal waves can travel through

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18
Q

How does the sun’s heat reach us if space is a vacuum?

A

Transverse waves because they don’t need particles

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19
Q

Identify a factor affecting the speed of sound

A

The closer together the atoms (denser), the quicker sound travels

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20
Q

Define density

A

The amount of matter in a certain volume of a substance

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21
Q

Order glass, water, steel, air and wood from most to least dense

A

Steel, Glass, Wood, Water, Air

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22
Q

How do you make sound from a guitar louder?

A

Plucking strings harder because it transfers more energy

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23
Q

What is the amplitude of a quiet noise?

A

Low

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24
Q

What is the amplitude of a loud noise?

A

High

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25
Q

How do you make pitch higher on a guitar?

A

Shorten strings because it transfers energy more quickly

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26
Q

What is the frequency of a low pitch sound?

A

Low

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27
Q

What is the frequency of a high pitch sound?

A

High

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28
Q

What are electromagnetic waves?

A

Electric and magnetic disturbances which are transverse waves which transfer energy from a source to an absorber. They travel through air or space at the same speed (constant speed of light)

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29
Q

What is the relationship between frequency and wavelength?

A

Higher the frequency, shorter the wavelength

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30
Q

What do electromagnetic waves form?

A

A continuous spectrum. The wavelength and frequency boundaries are approximate as different parts are not precisely defined

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31
Q

identify the 7 basic types of electromagnetic waves in order of increasing frequency/decreasing wavelength

A

Radio waves (1-10^4m), micro waves (10^-2), infra red (10^-5), visible light (10^-7), ultraviolet (10^-8), x rays (10^-10), gamma rays (10^-15)

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32
Q

Which is the portion of the continuous spectrum that is visible to the human eye?

A

Visible light. A typical human eye responds to wavelengths from about 380-740nm and light is 400-700nm

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33
Q

Why are there a large range of frequencies between EM waves?

A

They are generated by a variety of changes in atoms and their nuclei (e.g changes in the nucleus of an atom creates gamma rays). This is why atoms can absorb a range of frequencies - each one causes a different change

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34
Q

Frequency of light

A

4.3x10^14-7.5x10^14 Hz

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35
Q

What are electromagnetic waves made up of?

A

Oscillating electric and magnetic fields

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36
Q

When do EM waves travel at different speeds and what can this lead to?

A

In different materials, can lead to refraction

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37
Q

What are alternating currents made up of?

A

Oscillating charges which produce oscillating electric and magnetic fields e.g electromagnetic waves. The frequency of waves produced is equal to the frequency of the alternating current

38
Q

How can you produce radio waves? 6 steps

A

Use alternating current in an electrical circuit. The object in which charges oscillate is called a transmitter. When transmitted waves reach a receiver they are absorbed. Energy transferred by waves is transferred to electrons in material of the receiver. Energy causes electrons to oscillate and generates an alternating current if the receiver is part of a complete electrical circuit

39
Q

What is the relationship between frequency of current and frequency of the radio waves that created it?

A

They are the same

40
Q

What are radio waves used for?

A

Communication to transmit radiation, TV and mobile phone signals. Used to transmit signals instead of a cable (e.g wireless printer)

41
Q

How can long wave radio waves (1-10km) be transmitted and received halfway round the world?

A

Long wavelengths diffract (bend) around the curved surface of the Earth.

42
Q

How can long wave radio signals be received even if the receiver isn’t in line of sight of the transmitter?

A

Long wave radio wavelengths can diffract around hills and into tunnels

43
Q

How can short wave radio signals (10m-100m) be received long distances from the transmitter?

A

They are reflected from the ionosphere (an electrically charged layer in the Earth’s upper atmosphere

44
Q

Where must FM radio and TV signals be to be received and why?

A

Receiver must be in the line of sight of the transmitter because waves have very short wavelengths so cannot bend or travel far through buildings

45
Q

What can medium wave radio signals do?

A

Can also reflect from the ionosphere depending on atmospheric conditions and time of day

46
Q

Which type of electromagnetic wave is used in satellite communication?

A

Microwaves which can pass easily through the earth’s atmosphere

47
Q

How does a satellite TV receive a signal?

A

Signal from atransmitter sent into space where it is picked up from the satellite receiver dish orbiting thousands of kilometres above the earth. The satellite transmits the signal back to earth in a different direction where it is received by a satellite dish on the ground. Slight time delay between the signal being sent and received due to the long distance it has to travel

48
Q

Why may the properties of a microwave at one end of the range differ from one at the other end?

A

Each type of EM wave covers a spectrum of wavelengths and frequencies

49
Q

How do microwave ovens work?

A

Microwaves need to be absorbed by water molecules in food. They penetrate a few centimetres into the food before being absorbed and transferring energy they are carryingto water molecules in the food to heat it up. The water molecules transfer this energy to the rest of the food by heating which quickly cooks food

50
Q

What is white light?

A

Contains all colours of the spectrum (as seen in a rainbow) which goes from red to violet as wavelength increases

51
Q

What is the difference between wavelengths of microwaves and radio waves?

A

Microwaves have shorter wavelengths

52
Q

What is infrared radiation emitted and absorbed by?

A

All objects. The hotter the object, the more IR radiation given out

53
Q

What are infrared cameras used for?

A

Detect infrared radiation and monitor temperature.The camera detects IR radiation and turns it into an electrical signal which is displayed on screen as a picture. The hotter the object, the brighter the picture

54
Q

What happens when objects absorb infra red radiation?

A

They get hotter so food can be cooked using IR radiation

55
Q

How do electric heaters work?

A

They contain a long piece of wire that heats up when a current flows through it. This wire then emits lots of infra red radiation (and a little visible light as it glows). The emitted infrared radiation is absorbed by objects and the air in the room - energy is transferred by IR waves to the thermal energy stores of the objects which causes their temperature to increase

56
Q

How can you measure the speed of sound? 4 points

A

Set up an oscilloscope so detected waves at two different microphones are shown as separate waves, place both microphones next to a speaker attached to a signal generator then slowly move one away until the two waves are aligned on the display but have moved exactly one wavelength apart, measure the distance between the microphones to find the wavelength, use formula v=f x lambda to find the speed of sound waves passing through air (the frequency is whatever you set the signal generator attached to the speaker to)

57
Q

How can you measure the speed of water ripples? 4 points

A

Dim the lights and turn on a lamp above the ripple tank to see a wave pattern made by the shadows of wave crests on the screen below the tank, the dipper of a ripple tank is attached to a signal generator and dips in and out to produce ripples, the distance between each shadow is equal to the wavelength so measure the distance between shadow lines that are 10 wavelengths, use v =f x lambda to calculate speed

58
Q

How can you measure waves on strings? 6 points

A

On a bench place a signal generator attached to a vibration transducer (which converts signals to vibrations) attached to a string attached to a pulley with masses on the end, adjust the frequency setting on the signal generator to change the length of the wave created on the string until there appears to be a clear wave on the screen which happens when a whole number of wavelengths fit on the screen (4 or 5 ideally), frequency you need depends on the length of string between the pulley and transducer and the masses used, measure the wavelength of the wave by measuring the length of all the half wavelengths in one go then divide by the total number of half wavelengths to get the mean half wavelength then double this value to get full wavelength, frequency is whatever you have set the signal generator to, use equation v=f x lambda to work out speed

59
Q

What is refraction?

A

Light waves are bent when they enter a new media

60
Q

What 3 things can happen when a wave arrives at a boundary between two different materials?

A

Wave is absorbed by the second material so energy is transferred to the material’s energy stores often the thermal energy stores so heating occurs, wave is transmitted through the second material so waves carry on travelling through which often leads to refraction, the wave is reflected so is sent back away from the second material

61
Q

What 2 things is refraction used for?

A

Communications, lenses of glasses and cameras

62
Q

What 2 things does what happens when a wave arrives at a boundary between two different materials depend on?

A

Wavelength of wave, properties of the material

63
Q

How does refraction occur? 5 points

A

When a wave crosses a boundary between two materials it changes speed, if it is travelling along the normal it will change speed but is not refracted as it carries on in the same direction, if it hits the boundary at an angle it changes direction so is refracted, the wave bends towards the normal if it slows down, the wave bends away from the normal if it speeds up

64
Q

What is how much a wave is refracted by affected by?

A

Density of the 2 materials because this affects how much the wave speeds up or slows down, usually the higher the density the slower a wave travels through

65
Q

What happens to wavelength and frequency when a wave is refracted?

A

Wavelength changes but frequency stays the same

66
Q

What are rays?

A

Straight lines which are perpendicular to wave fronts

67
Q

How can you construct a ray diagram to show refraction? 5 points

A

Draw a boundary between two materials and the normal (90 degree line to boundary), draw an incident ray that meets the normal at the boundary, the angle between the ray and normal is the angle of incidence, draw the refracted ray on the other side of the boundary, if the second material is optically denser this ray will bend towards the normal so the angle of refraction would be smaller than the angle of incidence

68
Q

What happens to a wave front when a wave crosses a boundary?

A

A wave front is a line showing all of the points on a wave that are in the same position as each other after a given number of wavelengths. When a wave crosses a boundary at an angle only part of the wave front crosses at first and if it is travelling into a denser material this part travels slower than the rest of the wave front, by the time the whole wave front crosses the boundary the faster part of the wave front will have travelled faster than the slower part which causes the wave to bend/refract

69
Q

What are optical fibres and how do they work?

A

Thin glass or plastic fibres that can carry data (e.g from phones or computers) over long distances as pulses of visible light, they work due to reflection -the light rays are bounced back and forth until they reach the end of the fibre, light is not easily absorbed or scattered when it travels along a fibre

70
Q

What is fluorescence?

A

A property of certain chemicals where ultra violet radiation is absorbed then visible light is emitted -this is why fluorescent colours are so bright, they emit light

71
Q

What do fluorescent lights do?

A

Generate UV radiation which is absorbed and re emitted as visible light by a layer of phosphorus on the inside of the bulb, they’re energy efficient so good to use when light is needed for long periods

72
Q

What are security pens used for?

A

To mark property with your name, under UV light the ink will glow but is invisible otherwise, helps police identify your property if it is stolen

73
Q

How can x-rays be used to identify broken bones?

A

X-rays pass easily through flesh but not so easily through denser materials like bones or metal so the amount of radiation that isn’t absorbed gives you an x ray image (brighter bits are where fewer x-rays can get through, plate starts off all white), can diagnose dental problems like cracks and dental fractures

74
Q

How can x-rays and gamma rays be used to treat people with cancer? 2 ways

A

In radiotherapy these rays are directed carefully towards cancerous cells to kill or shrink tumours near the body’s surface but high doses can kill all living cells, gamma radiation can be used as a medical tracer where a gamma emitting source is injected into the patient and its progress is followed round the body then the radiation can be passed out the body to be dejected

75
Q

What are x rays used for with metals?

A

Identifying internal cracks

76
Q

Why are x rays dangerous?

A

Form of ionising radiation so can cause gene mutation and cell destruction, increasing exposure increases risk of mutations linked to cancer

77
Q

Why are UV rays dangerous? 4 reasons

A

Can cause blindness as they are harmful to eyes, can cause skin cancer, premature ageing and sunburn

78
Q

Define ionising power

A

Ability to make an atom lose an electron and form an ion. When some electromagnetic waves pass through a substance they knock out electrons from outer shells, If this happens in a living cell the cell can be killed or damaged

79
Q

What do people working with sources of radiation have to wear?

A

A film TDL badge which changes colour as it is sensitive to ionising radiation and it records radiation dose, if the badge shows over exposure the wearer is not permitted to continue working with the equipment for a period of time. Or they must wear a lead apron and stand behind a lead screen or leave the room to keep their exposure to a minimum

80
Q

Identify 3 uses of gamma radiation

A

Irradiating food (kills 99% of bacteria), radiotherapy, sterilisation of medical supplies

81
Q

How do x-rays work? 4 points

A

To make a x-ray photograph or radiograph x-rays from an x-ray tub are directed at the patient, a lightproof cassette containing a photographic film or a flat panel CCD detector is placed on the other side, when the x-ray tube is switched on x-rays pass through soft tissue but are absorbed by dense objects so these objects appear lighter on the x-ray than surrounding tissue, lead plates between the tube and patient stop x rays reaching other parts of the body as lead is a good absorber but x rays reaching the patient pa through gaps in the plates

82
Q

What is a CT scan?

A

Computed Tomography. X-rays are aimed at different parts of the body using a CCD detector to produce vertical slices of the body, uses a high dose of radiation

83
Q

Which are cheaper: MRI scans or CT scans?

A

CT scans as MRIs use magnets not ionising radiation

84
Q

What is radiation dose?

A

Measure of the risk of harm from the body being exposed to radiation, not a measure of the total amount of radiation that has been absorbed, the risk depends on the total amount of radiation absorbed and how harmful the type of radiation is, doses are often in millisieverts (1000mSv = 1sievert)

85
Q

Compare radiation dose of CT scans to the head and chest

A

If a patient has a CT scan on their chest they are four times more likely to suffer damage to their genes and their added risk of harm is four times higher than if they had had a head scan

86
Q

What does an object that is hotter than its surroundings do?

A

Emits more IR radiation than it absorbs as it cools down whereas an object at a constant temperature emits infrared at the same rate it is absorbing it

87
Q

Which surfaces are the best emitters and absorbers?

A

Black and matte rather than white and shiny

88
Q

What experiment can you do to prove that the amount of IR radiation absorbed depends on the material? 3 points

A

Face the silver side of a plate and the matt black side of another plate towards a bunsen burner, two ball bearings are stuck to the other sides of the metal plate with solid pieces of candle wax, ball bearing on the black plate will fall first as the black surface absorbs more IR radiation which transfers more energy to the thermal energy store of the wax so this wax melts first

89
Q

How can you investigate emission? 6 points

A

Place an empty leslie cube, boil water in a kettle and fill the leslie cube with boiling water, wait for the cube to warm up and hold a thermometer to each four walls which will be the same temperature, hold an infrared detector a set distance away from one of the cube’s vertical faces and record the amount of IR radiation it detects, repeat this measurement for each of the cube’s vertical faces and position the detector at the same distance from each one, you should detect more IR radiation from the black and matt surfaces

90
Q

What is a leslie cube?

A

Hollow watertight metal cube made of aluminium for example whose four vertical faces have different surfaces like matt black paint & matt white paint & shiny metal & dull metal, used to investigate IR radiation emitted by different surfaces

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