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Physics > Topic 6: Waves > Flashcards

Topic 6: Waves Flashcards

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1
Q

Direction of vibrations in a transverse wave

A

Perpendicular to direction of energy transfer

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2
Q

Direction of vibrations in a longitudinal wave

A

Parallel to direction of energy transfer

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3
Q

Examples of transverse waves [2]

A
  1. All electromagnetic waves
  2. Ripples in water
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4
Q

Examples of longitudinal waves [2]

A
  1. Sound waves
  2. Shock waves
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5
Q

Define ‘amplitude’ of a wave

A

Maximum displacement of a point on the wave from its undisturbed position

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6
Q

Define ‘wavelength’ of a wave

A

Distance between the same point on two adjacent waves

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7
Q

Define ‘frequency’ of a wave

A

Number of complete waves passing a point per second

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8
Q

Do waves transfer matter?

A

No, they transfer energy without transferring any matter

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9
Q

Briefly describe how you would measure the speed of sound in air? [6]

A
  1. Attach a singal generator to a speaker
  2. Set up a oscilloscope so that the detected waves of each microphone are shown as separate waves
  3. Start with both microphones next to the speaker
  4. Slowly move one microphone away until the two waves are aligned on the display, but have moved one wavelength apart
  5. Measure the distance between the microphones to find one wavelength
  6. Use the formula to find the speed of the sound waves
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10
Q

What 3 things can happen when a wave hits a boundary?

A
  1. Absorbed
  2. Transmitted
  3. Reflected
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11
Q

What happens when a wave is absorbed by a material?

A

The energy from the wave is transferred to the material’s energy stores

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12
Q

What happens when a wave is transmitted by a material?

A

The wave carries on travelling through the new material (often leads to refraction)

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13
Q

What happens if a wave is reflected by a material?

A

Wave reflects off the material at the same angle it entered

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14
Q

What 2 things determine if a wave is absorbed, transmitted or reflected?

A
  1. Wavelength of wave
  2. Properties of materials involved
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15
Q

What is specular reflection?

A

When a wave is reflected in a single direction by a smooth surface

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16
Q

What is diffuse reflection?

A

When a wave is reflected by a rough surface and the reflected rays are scattered in many different directions

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17
Q

Why does diffuse reflection cause the rays to scatter?

A

The normal is different for each incoming ray, which means the angle of incidence is different for each ray

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18
Q

What happens when a wave enters a more dense material?

A

It slows down and bends towards the normal

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19
Q

What happens when a wave enters a less dense material?

A

It speeds up and bends away from the normal

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20
Q

What happens if a wave is travelling along the normal and enters a different density?

A

It will change speed but NOT be refracted

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21
Q

Name the electromagnetic spectrum [7]

A

Radio waves, micro waves, infrared radiation, visible light, ultraviolet light, x-rays, gamma rays

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22
Q

What is the rule as you go along the EM spectrum?

A

Increasing frequency and decreasing wavelength

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23
Q

How are radio waves produced?

A

By oscillations in electrical circuits

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24
Q

How would you generate a radio wave? [6]

A
  1. Connect a transmitter to an oscilloscope
  2. The frequency of the ac can be seen on the screen
  3. The radio wave is generated and is detected by a receiver
  4. The receiver absorbs the energy and creates another ac
  5. This ac is then displayed on another oscilloscope
  6. The frequency received is the exact same as the frequency used to generate the wave
25
Q

Why can long-wave radio be detected in different parts of the world?

A

Long wavelengths can bend around the curved surface of the Earth

26
Q

How is short-wave radio transmitted?

A

They are reflected from the ionosphere

27
Q

What is an example of short-wave radio?

A

Bluetooth

28
Q

What must you do to get a signal from very short-wave radio?

A

Be in direct sight of the transmitter

29
Q

Why does communication via satellites use microwaves?

A

They can pass through the Earth’s watery atmopshere without being absorbed

30
Q

Briefly describe how satellite TV works [4]

A
  1. Signal from a transmitter is transmitted into space
  2. It is picked up by a satellite receiver dish
  3. Satellite transmits signal back to Earth in a different direction
  4. It is received by a satellite dish
31
Q

How do microwaves heat up food? [6]

A
  1. Microwaves penetrate a few centimetres into the food
  2. They are absorbed by water molecules
  3. Transfer their energy to these water molecules
  4. The water heats up
  5. Water molecules transfer this energy to the rest of the food molecules by heating
  6. Food heats up
32
Q

What is infrared radiation given out by?

A

All hot objects

33
Q

How do infrared cameras work?

A

Camera detects IR radiation and turns it into an electrical signal which is displayed on the screen as an image

34
Q

How does IR radiation heat up food?

A

IR radiation is produced from the heating element (toaster) which the food absorbs

35
Q

How do electrical heaters use IR radiation? [5]

A
  1. Long piece of wire heats up
  2. Wire emits lots of IR radiation
  3. IR radiation is absorbed by the objects and air
  4. Energy is transferred by IR waves to thermal stores of the objects
  5. Temperatures increase
36
Q

What are optical fibres?

A

Thin glass or plastic fibres that carry data as pulses of visible light

37
Q

How do optical vibres transmit data using visible light?

A

Light rays are reflected along the fibre

38
Q

How do fluorescent lights work?

A

They absorb UV radiation and re-emit it as visible light

39
Q

Explain how x-rays are produced

A

X-rays pass esaily through flesh but not so easily through denser materials (bone). The amount of radiation absorbed by the plate gives you the x-ray image

40
Q

What colour does an x-ray plate start off as?

A

White

41
Q

Why is gamma radiation used in medical tracers?

A

It can pass through the body and be detected

42
Q

How is the colour of an opaque object determined?

A

By which wavelengths of light are most strongly reflected

43
Q

Why does an object appear white?

A

All of the wavelengths of visible light are being reflected equally

44
Q

Why does an object appear black?

A

All of the wavelengths of visible light are absorbed

45
Q

What determines the colour of a translucent object?

A

Which wavelength of light is transmitted the most strongly

46
Q

What do colour filters do?

A

Absorb certain wavelengths and transmitting other wavelengths

47
Q

What would you see if you looked at white paper through a green filter (and why)?

A

It would appear green because only green waves are transmitted and the others are absorbed

48
Q

What would happen if you looked at blue paper through a green filter (and why)?

A

It would appear black because the filter has prevented the blue light from being transmitted

49
Q

What is a perfect black body?

A

An object that absorbs all of the radiation that hits it

50
Q

Why can’t sound travel through a vacuum?

A

Because there are no particles to move or vibrate

51
Q

What is the human hearing range?

A

20Hz - 20,000Hz

52
Q

Explain what happens when sound waves enter your ear [4]

A
  1. Sound waves reach your eardrum and cause it to vibrate
  2. Vibrations are passed onto the ossicles, semicircular canals and to the cochlea
  3. Cochlea turns these vibrations into electrical signals
  4. Signals get sent to your brain via the auditory nerve
53
Q

What is ultrasound?

A

Sound with frequencies higher than 20,000Hz

54
Q

How does ultrasound work? [2]

A
  1. Ultrasound waves pass through the body, but whenever they reach a new boundary between two different media some of the wave is reflected back and detected
  2. The exact timing and distribution of these echoes are processed by a computer to produce a video image of the foetus.
55
Q

How can ultrasound be used to find flaws in objects? [2]

A
  1. Ultrasound waves entering a material will usually be reflected by the far side of the material
  2. If there is a flaw such as a crack inside the object then the wave will be reflected sooner than expected
56
Q

Properties of P waves [3]

A
  1. Longitudinal
  2. Can travel through solids and liquids
  3. Travel faster than S-waves
57
Q

Properties of S waves [3]

A
  1. Transverse
  2. Can only travel through solids
  3. Slower than P-waves
58
Q

How were scientists able to discover the internal structure of the Earth?

A

By measuring which types of waves could be detected at different places around the Earth

Physics (8 decks)

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