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Physics > Waves & Optics 1 > Flashcards

Waves & Optics 1 Flashcards

1
Q

How do waves transfer energy?

A

Without transferring any matter.

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2
Q

What happens when waves travel through a medium?

A

The particles of the medium oscillate and transfer energy between each other.
However, the particles stay in the same place - Only energy is transferred, not matter.

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3
Q

Describe wave motion in experiments using water waves?

A

You can demonstrate waves using water in the ripple tank.
The wave pattern can be seen more clearly if a lamp is positioned so light shines down through the ripple tank.
This casts shadows of the waves on the screen below the tank.

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4
Q

Describe wave motion using a rope?

A

Wiggle one end of the rope quickly.
A wave pulse will travel down the rope towards the other end.
If you keep wiggling, you will see a continuous wave.

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5
Q

What is the wavelength?

A

The distance between the same point onto two adjacent waves.
E.g. between the trough of one wave and the wave next to it.

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6
Q

What is the frequency of a wave?

A

The number of complete waves, passing a certain point per second.
Measured in Hertz.

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7
Q

What is 1 Hz?

A

1 Hz is one wave per second.

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8
Q

What is the amplitude of a wave?

A

The maximum displacement of point on the wave from its undisturbed position.

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9
Q

What is the equation for wave speed?

A

Wave speed = frequency * wavelength

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10
Q

What is the wavefront?

A

A top down view of the peaks of the wave.

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11
Q

Define a wave?

A

An oscillation that transfers energy, plus information, but not matter.

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12
Q

What is the time period?

A

The time for one full wave cycle.

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13
Q

Define a transverse wave?

A

Oscillations are perpendicular to the direction in which the wave is propagated.

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14
Q

What are examples of transverse waves?

A

All electromagnetic radiation waves.
Seismic S-waves.
Water waves.

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15
Q

Define a longitudinal wave?

A

Oscillations are parallel to the direction in which the wave is propagated.
Longitudinal waves have compressions and rarefactions.

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16
Q

What are examples of longitudinal waves?

A

Pushing the end of the spring.
Sound waves in air.
Seismic P-waves.

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17
Q

What can waves undergo?

A

Reflection at a plane surface.
Refraction due to a change of speed.
Defraction through a narrow gap.

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18
Q

Describe how a ripple tank shows reflection?

A

Reflection can be shown by the waves hitting a plane surface, such as a wall or a mirror.

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19
Q

Describe how a ripple tank shows a refraction?

A

Refraction can be shown by placing a glass block in the tank.
The depth of water becomes shallow where the glass block is placed.
Speed depends on depth, so the ripples slow down when travelling over the block.
This is a good model of refraction, showing how waves slowdown when passing from deep water into shallow water.

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20
Q

Describe how a ripple tank shows diffraction?

A

Defraction can be shown in a ripple tank by placing small barriers and obstacles in the tank.
As the water waves encounter to obstacles with a gap between them, the waves can be seen to spread out.

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21
Q

Describe diffraction through a narrow gap?

A

Large diffraction if wavelength is larger/equal to gap.

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22
Q

Describe diffraction through a wide gap?

A

Small diffraction if the wavelength is smaller than gap.

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23
Q

Describe the diffraction of water waves after passing an edge?

A

The amount of diffraction depends on the size of the gap compared to the wavelength of the water wave.
The higher the frequency of the motor, the shorter the wavelength.
The lower the frequency of the motor, the longer the wavelength.

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24
Q

How does the wavelength affect diffraction around an edge?

A

A longer wavelength means a greater diffraction.

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25
Q

Name the electromagnetic spectrum regions in order of increasing frequency?

A

Radio
Micro
Infrared
Visible light
Ultraviolet
X-ray
Gamma

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26
Q

Name the regions of the electromagnetic spectrum in order of decreasing wavelength?

A

Gamma
X-ray
Ultraviolet
Visible light
Infrared
Microwave
Radio

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27
Q

What are the relative speeds of electromagnetic waves in the vacuum?

A

All electromagnetic waves travel at the same speed

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28
Q

What are the uses of radio waves?

A

Radio
TV transmissions
Astronomy
RFID - allows objects to be identified through transfer of data

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29
Q

What are the uses of microwaves?

A

Satellite television
Mobile phones
Microwave ovens

30
Q

What are the uses of infrared radiation?

A

Electric grills
Short range communications - remote controllers for TVs
And food alarms
Intruder alarms
Thermal imaging
Optical fibres

31
Q

What are the uses of visible light?

A

Vision
Photography
Illumination

32
Q

What are the uses of ultraviolet rays?

A

Security marking
Detecting fake bank notes
Sterilising water

33
Q

What are the uses of x-rays?

A

Medical scanning
Security scanners

34
Q

What are the uses of gamma rays?

A

Sterilising food and medical equipment
Detection of cancer and its treatment

35
Q

What are the harmful effects of microwaves?

A

Internal heating of body cells

36
Q

What are the harmful effects of infrared rays?

A

Skin burns

37
Q

What are the harmful effects of ultraviolet rays?

A

Damage to surface cells and eyes – leading to skin cancer and eye conditions.

38
Q

What are the harmful effects of x-rays and gamma rays?

A

Mutation or damage to cells in the body – leading to cancer.

39
Q

What is the speed of electromagnetic waves/light in the vacuum?

A

3×10 power of 8 m/s

40
Q

How does communication with artificial satellites occur?

A

By microwaves

41
Q

Describe low orbit satellites?

A

Sweep relatively low over the Earth.
They move very fast.
Because they are so close to the Earth and orbit, so quickly, you need multiple satellites, working together to maintain constant coverage.

42
Q

Describe geostationary satellites?

A

Have a high orbit over the equator & orbit once every 24 hours.
They stay at the same point above the Earth because they orbit at the same speed as the Earth.
So they are ideal for communications as it’s easy to point transmitters and receivers at them.
They can transfer signals from one side of the Earth to the other in a fraction of a second.

43
Q

What types of satellites do satellite phones use?

A

Both low orbit satellites & geostationary satellites.

44
Q

What type of satellite does satellite television use?

A

Geostationary satellites.

45
Q

What is the advantage of using satellite phones over normal mobile phones?

A

Satellite phones work all over the planet.
They are not limited to areas covered by normal mobile phone masts.

46
Q

How is satellite television data transmitted?

A

By microwave signals from a large antenna on the ground to the receiver dish of a geostationary satellite in space.
The satellite then transmits the data directly to satellite dishes on the roof of individual homes.

47
Q

Why do mobile phones and wireless Internet use microwaves?

A

Microwaves can penetrate some walls and only require a short aerial for transmission and reception – they can be carried around easily.

48
Q

Why does Bluetooth use low energy radio waves or microwaves?

A

They can pass through walls, but the signal is weakened on doing so.
This reduces interference between devices which are using Bluetooth at the same time.

49
Q

Why are optical fibres (visible light or infrared) used for cable television and high-speed broadband?

A

Gloss is transparent to visible lights, and some infrared – visible light and short wavelength infrared can quickly carry high rates of data.

50
Q

What is the difference between an analogue and a digital signal?

A

Analogue signals can have any value within range – they show continuous variation.
But digital signals can only take certain values.

51
Q

How can a sound be transmitted?

A

As a digital or an analogue signal.

52
Q

How can you turn an analogue signal into a digital signal?

A

By digitising the signal.
Take the value of the analogue signal at regular time interval and find the nearest digital value.

53
Q

What are the advantages of using digital signals?

A

Digital signals can be sent over a greater range than analogue signals without loss of quality.
Over a distance, electronic signals, pick up noise and get weaker – signals can be amplified, but the noise is amplified too.
The receiver needs to reconstruct the original signal and remove the noise through regeneration.
Regeneration is much more accurate with the digital signals, because the number of values and digital signals can take is a limited.
Digital signals transmit data at a faster rate than analogue signals – with the radio more programs can be transmitted with a higher quality sound.

54
Q

Describe how soundwaves are produced?

A

By vibrating objects.

55
Q

Describe the longitudinal nature of soundwaves?

A

Vibrations are passed through the surrounding material as a series of high density areas and low density areas – sound is a type of longitudinal wave.

56
Q

Describe compression and rarefaction?

A

Compression – area of high density.
Rarefaction – area of low density.

57
Q

What is the range of frequencies audible to humans?

A

20 Hz to 20,000 Hz

58
Q

Why do soundwaves have to travel through a medium?

A

Because they are made up of vibrating particles.

59
Q

What is the speed of sound in air?

A

330–350 m/s

60
Q

Why can’t sound travel in space?

A

Because space is a vacuum, so there are no particles to move or vibrate.

61
Q

Describe the different speeds of sound?

A

Solid > liquids > gases

62
Q

Describe a method to determine the speed of sound in air?

A

Set up two microphones several metres apart and place a source of sound so that they are all along the same line.
Measure the distance between the microphones.
Set up the data logger so that it records the time that the sound reaches each microphone.
Use these values to calculate your answer.

63
Q

How do changes in amplitude affect the loudness and pitch of soundwaves?

A

A greater amplitude means more energy is transferred.
For sound waves this means it will be louder.
Change in amplitude has no effect on pitch.

64
Q

How do you changes in frequency affect the loudness and pitch of soundwaves?

A

A high frequency means a high-pitch and a low frequency means a low pitch.
Frequency has no effect on amplitude.

65
Q

Describe an echo?

A

A reflection of sound waves.

66
Q

Why do empty rooms echo more?

A

Because items of furniture absorb soundwaves quickly and stop them reflecting and echoing around the room.
This is because soundwaves are reflected by hard flat surfaces.

67
Q

Why is there a delay between the original sound and the echo?

A

Could soundwaves have to travel further, so they take longer to reach your ears.

68
Q

Define ultrasound waves?

A

Soundwaves with a frequency greater than 20,000 Hz.

69
Q

Describe the medical uses of ultrasound?

A

Ultrasound waves can pass through the body, but upon reaching a boundary between two different mediums, some of the wave is reflected back and detected.
The exact timing and distribution of these echoes are processed by a computer to produce an image of structures inside the body.

70
Q

Describe the industrial uses of ultrasound?

A

Testing materials in a non-destructive way – finding flaws in wood or metal.
Ultrasound waves entering the material will usually be reflected by the far side of the material – if there is a flaw like a crack inside the object, the wave will be reflected sooner.

71
Q

Describe how sonar by ships works?

A

A pulse of sound waves is directed at the seafloor.
The depth of the sea beneath the vessel can be calculated using the time it takes to detect the reflected pulse.

Physics (10 decks)

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