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Physics > Section 2 - Waves and The Electromagnetic Spectrum > Flashcards

Section 2 - Waves and The Electromagnetic Spectrum Flashcards

1
Q

What do waves transfer?

A

energy and information in the direction they are travelling

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2
Q

What is the amplitude of a wave?

A

The displacment from the rest position to a crest or trough

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3
Q

What is the wavelength of a wave?

A

length of afull cycle of a wave ( crest to crest )

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4
Q

What is the frequency of a wave?

A

the number of complete cycles of wave passing a cartain point per second

Mesured in Hz

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5
Q

What is the period of a wave?

A

the number of seconds it takes for one full cycle

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6
Q

What way do transverse waves vibrate?

A

Sideways, the vibrations are at 90degrees to the direction of the wave travel

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7
Q

What are some examples of transverse waves?

A

All electro magnetic waves
S waves
ripples and waves in water

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8
Q

what way do longitudinal waves vibrate?

A

parralel vibrations to the direction of the wave travel
They extend and compress

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9
Q

What are some examples of longitudal waves?

A

sound waves
P waves

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10
Q

What 3 things can happen to waves at boundaries?

A

Absorbed
Transmitted
Reflected

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11
Q

Wave ABSORBED

A

the wave transfers energy to the materials energy stores

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12
Q

Wave TRANSMITTED

A

the wave carries on travellign throughthe new material. This often leads to refraction

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13
Q

Wave REFLECTED

A

the incoming ray is neither absorbed or transmitted but instead is sent back “away” from the second material

Echos

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14
Q

What is Ultrasound?

A

sound with frequncies higher than 20,000Hz.

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15
Q

What happens to Ultrasound waves at boundaries?

A

They get partially reflected at boundaries ( some of the wave is reflected off )

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16
Q

What are some usefull ways to use Ultrasound? Why?

A

Pre-natal scanning of foetus
Industrial imaging

this is because when ultrasound reaches a medium boundary it is partially reflected. This reflection can be processed into a scan.

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16
Q

what is Infrasound?

A

Sound with frequencies lower than 20hz

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17
Q

What are some examples of Infrasound?

A

Whales and ELephants use it so communicate, this can be picked up and used to track these animals
Infraosund (seismic waves ) is released before an earthquake so scientists can pedict when the earthquak is going to happen

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18
Q

What are the two examples of Seismic waves?

A

P waves and S waves

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19
Q

P waves

A

They are LONGITUDINAL
they travel through solids and liquids
They travle faster than S waves

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20
Q

S waves

A

TRANSVERSE
onyl travle through solids
they are slower than P waves

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21
Q

What is the total intertial reflection

A

at what angle all of the wave is reflected
- Only happens when going from dense -> less dense material.

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22
Q

transparent vs translucent

A

When going through a transparent matter, the light rays stay parralel to eachother. Whereas when going through a translucent matter, the waves are scattered ( this means you cant see a clear image

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23
Q

When from a fast object to a slow one…

A

Light refracts towards the normal

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24
Q

When from a slow object to a fast one…

A

light refracts away from the normal

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25
Q

what is white light?

A

a mixture of all the different colours of light

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26
Q

What do opaque object do?

A

they do not transmit light.
They absorb some wavelengths of light and reflect others

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27
Q

Why do opaque objects have color?

A

They absorb some wavelengths of light, and refect other wavelengths, the wavelenghts corresponging to the visible spectrum reflected are the color the object is.

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28
Q

Transmit

A

to pass through

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29
Q

What do white objects do?

A

Reflect all wavelengths of visible light equally

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30
Q

What do black objects do?

A

absorb all wavelenths of visible light
- are a lack of visible light

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31
Q

Transparent

A

See through

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32
Q

translucent

A

partially see through

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33
Q

What do transparent and translucent objects do?

A

Transmit light - they appear as the color they most strongly transmit

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34
Q

Color filters

A

only let particular wavelenths through
- used to filter out different wavelengths of light, and therefore onyl let certain ones through
- if a color is not transmitted through the filter the object will appear black

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35
Q

EM waves

A
  • spectrum grouped on wavelength and frequency
  • transverse
  • all travel at the same speed in a vacuum but travel at different speeds in different materials
  • Vary in wavelength
  • eyes can only see the visible light
  • transfer energy from a source to an absorber
  • Higher frequency = more energy
36
Q

What are the three sections of the EM spectrum with long wavelengths?

A

Radio waves
Micro waves
Infrared

37
Q

What are the three sections of the EM spectrum with short wavelengths?

A

Ultra violet
X rays
Gamma rays

38
Q

Radio wave - Heath implications

A

transmitted throught he body without being absorbed- safe

39
Q

Micro wave - Heath implications

A

Some wavelengths can be absorbed, causing heating of cells - may be dangerous

40
Q

Infrared and Visible light - Heath implications

A

Mostly reflected or absorbed by skin, causing some heating. IR can burn

41
Q

Ultra Violet- Heath implications

A

Absorbed by skin but because it is a higher frequency is more dangerous.
- ionising radiation - when absorbed an cause damage to cells on the surface of skin -> can lead to cancer
- can damage your eyes - eye conditions and blindness

42
Q

X rays and Gamma rays- Heath implications

A
  • Ionising radiation - can cause mutations and damages to cells -> cancer
  • High frequency - high damage
  • can pass through skin and be absorbed by deeper tissues
43
Q

What is the order of the EM spectrum

A

Radio waves
Micro waves
Infrared
Visible light
Ultra Violet
X rays
Gamma rays

44
Q

Power

A

energy transferred per second

mesured in W

45
Q

Intensity

A

Power per unit area

46
Q

Visible light - uses

A

Light bulbs are designed to emit it
Cameras detect it and use it to capture images

47
Q

Infrared - uses

A
  • Communication at short distances
  • Optical fibres
  • Grills or toasters uses them to heat things up
  • thermal imaging -> Security systems
48
Q

Microwaves - uses

A
  • Communications ( mobile phone signals )and sattelite transmittions
  • Microwave oven - heating food
49
Q

Radiowaves - uses

A
  • transmitting radio broadcasts ( sattelites)
  • ground -> spacecraft
50
Q

how are Radiowaves produced

A

Produced by oscillating currents in electrical circuits - also can cause these

51
Q

Oscillate

A

go back and forwards

52
Q

Oscillating currents

A

Electrons moving backwards and forwards

53
Q

What path do waves travel in?

A

Straight lines unless reflected or refracted

54
Q

Refraction

A

the bending of a path due to a change in velocity

55
Q

The Ionosphere

A

The top part of the atmosphere
Some radiowaves and all microwaves pass through it
- if radiowaves reach the ionosphere at a suitible angle, they can be refracted back, allowing further travel.

56
Q

radiation and temperature

A

The intensity of radiation emitted by an object increases as it temperatures increases, the wavelengths also change with temp - Higher temp = more energy = shorter wavelength

57
Q

Radiate

emit

A

energy coming out of stuff

58
Q

absorb

A

energy coming into stuff

59
Q

Cold

A

absence of heat energy
colder things will absorb more heat

60
Q

How can something stay at a constant temperature?

A

It must absorb the same amount of heat energy it radiates
- Heat will spread from high temp to low temp untill a thermal equilibrium is reached

61
Q

The earths energy balance

A
  • absorbs about 1/2 the radiation t recves from the sun
    • radiates it as infrared
62
Q

The greenhouse effect

A

Some gases in our atmosphere ( mainly CO2 ) naturally abosrb some energy, keeping the earth at a higher temperature than if there were no atmosphere

63
Q

Specular

A

Waves are reflected in a single direction by a smooth surface - clear reflection

64
Q

Diffuse

A

Waves reflected by a rough surface are reflected in all directions - matt, no reflection

65
Q

Ultra-violet uses

A

Flourescent lamps
Sterilise water - kills bacteria

66
Q

X-rays uses

A

for x-ray images in hospitals or airport security scanners

67
Q

Gamma rays uses

A

Sterilise medical instruments - kill microbes
Cancer scanning or treatments

68
Q

What us ultrasound and its uses?

A

Sound with frequencies higher than 20 000 Hz
- Foetal scanning
- Industrial imaging

69
Q

What is infrasound?

A

Sounds with frequencies lower than 20hz
- Some animals such as whales use this to communicate

70
Q

What EM has the highest frequency?

A

Gamma

71
Q

What EM has the highest wavelength?

A

Radiowaves

72
Q

Does Wave speed change throughout the EM spectrum in a vaccum?

A

no

73
Q

How do you calculate Wave speed?

A

Distance/Time
or
Wavelength x frequency

74
Q

What do you use to mesure the speed of sound?

A

Oscilloscope

75
Q

Explain the practical to mesure the speed of sound

A

Attach a signal generator to a speaker so it can release sound waves with specific frequencys
1. Set up an Oscilloscope attached to two microphones so the waves from each microphone are seperate
2. Start with both microphones next to the speaker, then slowly move one away untill the two waves are aligned, but one is exactly one wavelength apart
3. Mesure the distance between the microphones to find one wavelength
4. Then use v = fλ fo find the wavespeed, th frequency is whatever you set the speaker to

76
Q

Explain the experiment to mesure the speed of water ripples using a strobe light

(Liquids only)

A
  1. Using a signal generator attached to the dipper of the water tank, create water waves at set frequency
  2. Dim the lights and turn on the strobe light to see a wave pattern made by the shadows of the crests of the waves
  3. Alter the strobe light’s frequency untill the wave pattern appears to stop moving - this is when the frequency of the wave is the same as the strobes ( lit at same point in cycle each time)
  4. Mesure wavelength (Dist between shadows) and find average of 10
  5. Use v = fλ to find the wavespeed

Find frequency by calc waves passed a point in a set time (normal light)

77
Q

Describe the THEORY behind the experiment using peak frequency to find the speed of waves in solids

(for solids)

A

Can do this by mesuring the frequency of sound waves when you hit an object e.g a rod with a hammer. Hitting the rod causes waves to be produced along the rod. These waves make the rod vibrate and produce sound waves in the air around the rod. These sound waves have the same frequencies as the waves in the rod

78
Q

Describe the experiment using peak frequency to find the speed of waves in solids

A

1) Mesure and record the length of a rod
2) Set up clamps to hold elastic bands, holding up the rod, put a microphone at the end of the rod (leading to computer)
3) Tap the rod (other side of rod than microphone) with the hammer. Write down peak frequency displayed by the computer
4) do this X3 to get peak average frequency
5) Calc speed with v = fλ (λ is x2 length of rod)

79
Q

What happens when a wave hits a boundary of a different material

(not along the normal)

A

Different material density -> change in speed -> change in direction

This is called Refraction

80
Q

What happens when a wave hits a boundary of a different material along the normal

A

It will change speed but it is not refracted

81
Q

What happens at a boundary when there is a greater change in speed?

A

this causes a greater change in direction

82
Q

What happens to the speed of EM waves when they travel in denser materials?

A

they slow down

83
Q

How is an EM wave’s refraction affected by its wavelength?

A

Shorter wavelengths bend more
(this is why white light can refract into a spectrum)

84
Q

What happens to the frequency of a wave as it crosses a boundary, relating to v=fλ?

A

It stays the same, because there is a change in speed and v = fλ, this means that wavelength changes

85
Q

How does wavelength behave in a boundary when slowing down or speeding up?

A

Slowing down = λ decreases
Speeding up = λ increases

86
Q

How does the speed of sound change in different states

A

gases<liquids<Solids
- they can refract
- Will be reflected by hard, flat surfaces
- cant travel in a vacuum (no particles to vibrate)

Frequency doesnt change

87
Q
A
88
Q
A

Physics (7 decks)

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