Topic 2- Waves And Electromagnetic Spectrum Flashcards Preview

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Flashcards in Topic 2- Waves And Electromagnetic Spectrum Deck (84):
1

Transverse wave have vibrations which...

Are perpendicular to the direction the wave travels

2

Examples of transverse waves are...

All electromagnetic waves
S waves
Ripples and waves in water

3

Longitudinal waves have.... vibrations

Parallel vibrations to the direction the wave travels

4

What do longitudinal waves do to the particles

Squash up and stretch out the arrangement of particles in the medium they pass through
Therefore making compressions (high concentrations of particles- high pressure) and rarefactions (low concentrations of particles- low pressure)

5

Examples of longitudinal waves are...

Sound waves
P-waves

6

Waves transfer...

Energy and information in the direction they are travelling

7

When a wave travels through a medium...

The particles vibrate and transfer energy and information between each other up but overall the particles stay in the same place

8

Amplitude is...

The displacement from the rest position to a crest or trough

9

The wavelength is...

The length of a full cycle of the wave

10

Frequency is...

The number of complete cycles of the wave passing a certain point per second
Measured in hertz
eg. 1Hz is one wave per second

11

The period of a wave is...

The number of seconds it takes it takes for one full cycle

12

Period calculation

Period = 1 / frequency

13

Wave speed...

Tells you how quickly a wave moves through space
m/s

14

Two calculations for wave speed

Wave speed = distance / time

Wave speed = frequency X wavelength (called wave equation)

15

When a wave meets a boundary between two materials three things can happen...

Absorbed ... by the second material, the wave transfers energy to the materials energy store (often transferred to a thermal energy store, leading to heating eg. microwaves)
Transmitted ... through the second material, the wave carries on travelling through the new material (can be used in communications and lenses for glasses and cameras)
Reflected ... sent back away from the material (how echos are created)

16

Refraction occurs when...

A wave hits a boundary at an angle, this change of speed (because of change of density) causes a change in direction

17

Wave travelling along a normal...

No refraction
But change in speed

18

Greater the change in speed...

The more a wave bends (changes direction)

19

If the wave speeds up...
Slows down...

Speeds up... bends away from the normal
Slows down... bends towards the normal

20

How much EM waves refract is affected by...

Wavelength, shorter wavelengths bend more
Can lead to dispersion
eg.white light becoming a spectrum

21

Frequency... when crossing a boundary

Stays the same

22

Change of speed is caused by...

A change in wavelength
Wavelength decreases if the wave slows down and increases if the wave speeds up

23

Sound waves are...

Longitudinal waves

24

When sound waves travel through a solid...

It causes particles in the solid to vibrate, but not all frequencies can be transferred through an object

25

What determines which frequencies can be transmitted

Size, shape and structure

26

Sound travels ... in liquids than they do in gases and ...in solids than they do liquids

Faster in liquids than gas
Faster in solids than liquids

27

Sound waves wavelengths...

When slowed down they get shorter
When speeded up they get longer

28

Echos are...

Reflected sound waves
Sound waves will reflect at hard, flat surfaces

29

Sound waves in a vacuum

Sound waves can’t travel in a vacuum
Because there are no particles to move or vibrate

30

Eardrum

Causes the sound waves to vibrate

31

Ossicles...

Tiny bones which pass the vibrations through the semicircular canals and to the cochlea

32

The cochlea

Turns the vibrations into electrical signals which gets sent to the brain

33

Auditory nerve

Sends signals to the brain
The brain interprets the sound depending on the intensity and frequency
Eg. high frequency waves as high pitch sounds

34

Human hearing is limited...

By shale and size of eardrum
And structure of the parts that vibrate to transmit the sound wave

35

Ultrasound is...

A frequency of higher than 20,000 Hz

36

Ultrasound waves get...

Partially reflected and partially refracted

37

Uses for ultrasound

Medical imaging... scanning for a baby
Reach the womb, some waves get reflected others refracted and the exact distribution and timing of the echos produces an image of the foetus- completely safe

Industrial imaging... finding flaw in materials
Waves reflected by far side of material, if there is a flaw in the material the waves will be reflected sooner

Echo sounding
Underwater to find the distance to the seabed or locate objects in deep water

38

Infrasound is...

Frequencies lower than 20 Hz

39

Uses for infrasound

Some animals communicate using infrasound like elephants and whales
Erupting volcanos, avalanches and earthquakes produce infrasound, so scientists can study and monitor levels of infrasound to predict events
Earthquakes produce waves which travel through the different layers i of earth, some are infrasound, we can use these waves to explore the structure of the earth

40

Seismic waves are produced by...

Explosions and earthquakes at a range of frequencies which are spent through the earth

41

Seismic waves can be detected using a ...

Seismometer
Seismologists work out how long it take for the waves to reach the seismometer and what parts of earth don’t receive the waves

42

When seismic waves reach a boundary at the different layers in Earth...

The change of density and properties causes some of the waves to be absorbed and refracted

43

Mostly when the waves are refracted they change speed...

Gradually resulting in a curve path
When the properties change suddenly, the wave speed changes abruptly and the path has a kink

44

P-waves inside the earth are...

Longitudinal waves
Travel through solid and liquids
They travel faster than S-waves

45

S-waves inside the earth are...

Transverse waves
Only travel through solids
Slower than P-waves

46

Reflection angles rule...

Angle of incidence = Angle of reflection

47

Angle of incidence is...

The angle between the incoming wave and the normal

48

Angle of reflection is...

The angle between the reflected wave and the normal

49

The normal is...

The imaginary line that’s perpendicular to the surface at the point of incidence (the point the wave hits the boundary)

Shown as a dotted line

50

Total internal reflection is less than the critical angle...

Most of the last that is refracted into the outer layer, but some of it is internally reflected

51

Total internal angle is equal to the critical angle...

The ray would go along the surface
With quite a bit of internal reflection

52

Total internal reflection is larger than the critical angle...

No light comes out
It’s all internally reflected
i.e. total internal reflection

53

Total internal reflection is...

When a wave is reflected back into a material
Can only happen if the wave travels through a dense material like glass or water towards a less dense substance like air

54

Critical angle

Every material has its own, different critical angle

55

Speculator reflection is...

When waves are reflected in a single direction by a smooth surface
Means you get clear reflection
Eg. When light is reflected by a mirror

56

Diffuse reflection is...

When a wave is reflected by a rough surface (eg.paper) and the wave is reflected in all directions
This is because the normal is different for each incident ray, so each day has a different angle of incidence
Surface looks matt and you don’t get a clear reflection

57

White light is...

A mixture of all the different colours of light which all have different wavelengths

58

Opaque objects are objects that...

Do not transmit light
They absorb some wavelengths of light and reflect others

59

The colour of an opaque object depends on...

What wavelengths of light are reflected

60

White objects reflect...

All the wavelengths of visible light equally

61

Black objects absorb...

All wavelengths of visible light

62

Transparent

See through
Objects transmit light, not all the light is absorbed or reflected some...
Light can pass through

63

Translucent

Partially see through
Objects transmit light, not all the light is absorbed or reflected some...
Light can pass through

64

Colour filters are used to filter out...

Different wavelengths so only certain wavelengths (colours) are transmitted and the rest are absorbed

65

Converging lens

Bulges outwards in the middle
Causes parallel rays of light to be brought together t the principal focus
Convex lens

66

Diverging lens

Caves inwards in the middle
Causes parallel rays of light to spread out
Concave lens

67

Principal focus for converging and diverging lens

Principal focus of a converging lens is where the rays hitting the lens parallel to the axis all meet

Principal focus of a diverging lens is the point where rays hitting the lens parallel to the axis appear to all come from

68

A real image is...

Formed when the light rays actually come together to form an image
Can be captured on a screen
Eg. The image is formed on the eyes retina

69

A virtual image...

Is when the light rays from the object appear to be coming from a completely different place to where they’re actually coming from
Cannot be captured on a screen
Eg. Magnifying glasses create virtual images

70

Focal length is...

Related to the power of the lens
Eg. The more powerful the lens, the more strongly it converges rays of light, so the shorter the focal length

71

Power for converging and diverging lens

Converging lens - positive power
Diverging lens - negative power

72

Order of frequency and wavelength of the electromagnetic spectrum

Radio waves
Microwaves- Longest wavelength and lowest frequency
Infrared radiation
Visible light
Ultraviolet
X rays
Gamma rays- Shortest wavelength and highest frequency

73

Electromagnetic waves all travel through a vacuum at .......... but Tavel through different materials at ............

Same speed
Different speeds (leading to refraction and dispersion)

74

Colours of visible light in order of wavelength

Red
Orange - longest wavelength
Yellow
Glenn
Blue
Indigo
Violet - shortest wavelength

75

All electromagnetic waves transfer ..... from a ..... to an .......
The higher the frequency of an EM wave the ............ it transfers (making it ........... for humans)

Energy
Source
Observer
More energy
More dangerous

76

Radio waves and the human body

Are transmitted through the body without being absorbed

77

Microwaves and the human body

Some wavelengths can be absorbed causing a heating of cells which can be dangerous

78

Infrared and visible light and the human body

Are mostly reflected or absorbed by the skin causing some heating.
IR can cause burns if the skin gets too hot

79

Ultraviolet and the human body

Absorbed by the skin
More dangerous because of the higher frequency
Type of ionising radiation which means when it is absorbed it can cause damage to cells on the surface of you skin, can lead to skin cancer
Can damage eyes

80

X rays and gamma rays and the human body

Ionising, so can cause mutation and damage to cells
Higher frequencies cause even more damage
Deeper tissue can absorb the energy

81

The distribution and intensity of the wavelengths (of EM emitted and absorbed) ONLY depends on the objects...

Temperature

82

Intensity is...

The power per unit area

83

As the temperature of an object increase the intensity of every emitted wavelength ...

Increases

84

The intensity increases more rapidly for...
Causing what?

Shorter wavelengths
Causing the peak wavelength to decrease