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physics > waves > Flashcards

waves Flashcards

1
Q

Oscillate meaning of a wave

A

When a wave moves back and forth in repeating and regular way
(Another word for vibration)

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2
Q

Definition of transverse wave

A

Wave in which oscillations are perpendicular to the direction of energy transfer

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3
Q

Definition of longitudinal waves

A

Waves in which oscillations are parralel to direction of energy transfer

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4
Q

General definition of a wave

A

Transfers energy from one medium to the other without moving the medium in itself

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5
Q

Give five examples of transverse waves and two examples of a longitudinal wave

A

Transverse waves:
-light waves
-ripples on surface of water
-vibrations of guitar strings
- electromagnetic waves
- seismic S waves

Longitudinal waves
-sound waves
-seismic P waves

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6
Q

State why longitudinal waves can not move through a vacuum

A

Because they need particles to move

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7
Q

Definition of frequency

A

Number of complete waves in one second

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8
Q

Equation for wave speed

A

V (m/s) = f (hz)x lambda(m)

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9
Q

Give another way to express 1 hertz

A

1/T

Because F = 1/T

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10
Q

Time period meaning

A

Time taken for the number of complete waves to pass a point

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11
Q

Amplitude definition

A

The height of a wave, so distance between the rest point and the crest

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12
Q

Wavefront definition

A

Imaginary plane where vibrations are in phase and are the same distance from the source

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13
Q

Give two things that waves transfer

A

Energy and information

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14
Q

Give the structure of transverse waves, and the structure of longitudinal waves

A

Transverse waves= peaks and troughs
Longitudinal waves = rarefractiona and compressions

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15
Q

Give an example when the sound waves of a moving object are equally spaced:

A

When the object is moving at constant speed

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16
Q

When a wave source moves towards an observer, explain what they observe

A

Frequency is higher
Because wavefronts are more compressed
So wave length is shorter than original wave emitted
(And if sound, then pitch is higher)

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17
Q

Give the electromagnetic spectrum in order with up to three uses for each wave length

A

Radio waves—-) satellite communication AND radio + television
Microwaves—-)satellite communication AND cooking AND mobile phone calls
Infrared radiation—-) electric heating AND cooking AND temperature monitoring
Visible light—-)fibre optic communication AND photography
Ultraviolet——) fluorescent lamps AND sterilizes water
X-rays—-) medical imaging AND treatment
Gamma rays —-) sterilizing equipment + food AND destroying cancer cells

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18
Q

Comment on if these waves can move through a vaccum or not:
Longitudinal
Transverse

A

No longitudinal waves can travel through a vaccum
Only electromagnetic waves can travel through a vacuum for transverse waves

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19
Q

Explain the trend in properties of electromagnetic waves from radio waves to gamma rays(3)

A

Frequency increases
wave length becomes shorter
Energy transferred increases

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20
Q

What is special about electromagnetic waves and a vaccum

A

All travel at the same speed in a vacuum which is 3 x 10^8ms^-1

(And remember that they are the only transverse waves which can travel through a vacuum)

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21
Q

Which type of wave in electromagnetic spectrum has highest energy and which type of wave has lowest energy

A

Radio wave has lowest energy
Gamma ray has highest energy

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22
Q

Give four properties of all electromagnetic waves:

A

-all are transverse waves and are only transverse waves which can travel through a vaccum
-all travel at same speed through a vacuum which is 3 x 10^8ms
-transfer energy and not matter
-all can be reflected and refracted

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23
Q

Give the wave lengths of:
Radio waves
Visible light
Gamma rays

A

Radio waves: 1m-10^4m
Visible light: 10^-7m
Gamma rays: 10^-12m

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24
Q

How long are microwaves in centimeters

A

1cm

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25
Q

An ambulance is stood still with its siren on, and two people are stood on either side of it same distance apart

Explain the frequency that each person will hear

A

Both will hear same frequency
because there are evenly spaced wave fronts
And wave length distance is the same
So will hear same pitch

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26
Q

Give a source of gamma rays

A

Radioactive material

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27
Q

Give a source of visible light

A

Luminous objects

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28
Q

Give a source and detector of a radio wave

A

Source = radio transmitter
Detector= Aerial

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29
Q

Give a detector of visible light and a detector or infrared radiation

A

-the eye

And then

-a thermometer

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30
Q

Give a situation for radio waves in which
shorter wave length radio waves are used:
And longer wave length radio waves are used:

A

Shorter= Television and radio
Longer= satellite communication

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31
Q

Explain why microwaves cook food faster than ovens do

A

-because the water molecules in the food can quickly absorb the microwaves
-And so the heat energy can spread throughout in either conduction or convection(from centre to outside)
-rather than only cooking the outside of the food

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32
Q

Explain why microwaves have metal reflectors inside them

A

To keep waves inside the microwave
And prevent from reflecting outwards
Because microwaves can heat human body tissue

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33
Q

Explain why microwaves emitted from mobile phones are less dangerous than those emitted from real microwaves

A

Because microwaves emitted from phones carry less energy
And so can not harm human body tissue

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34
Q

Explain how waves are received from a satellite dish for satellite TV

A

-mircrowaves are released from transmitters
-microwaves travel through space
-satellite dish orbiting the earth picks up the signals

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35
Q

Which two electromagnetic waves sterilize equipment

A

Ultraviolet light and gamma rays

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36
Q

Give three uses of infrared radiation

A

Remote controls
Thermo monitoring
Cooking

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37
Q

Give two uses of radio waves

A

Broadcasting communication and radio/ television

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38
Q

Give three uses of microwaves

A

Satellite communication
Mobile phones
Cooking

39
Q

Give two uses of visible light

A

Photography
Fibre optic cables

40
Q

Give three uses of ultraviolet light

A

Fluorescent lamps
Sterilizes equipment
Security marker pens

41
Q

Give two uses of gamma rays

A

Sterilizes equipment
Can destroy cancer cells

42
Q

Explain why infrared radiation is good for remote controls

A

They only operate at small distances so will not interfere with other signals or waves

43
Q

Information stored on CDs and barcodes can be detected by which kind of electromagnetic wave?

A

Visible light

44
Q

Explain how fluorescent lamps emit visible light

A

When a current is passed,
Mercury vapour gives off UV rays
Which hit a coating on the tube, giving off white light

45
Q

Describe how X-rays are able to be formed

A

Because X-rays are able to travel through body tissue, but not bones

46
Q

Explain why it is important not to damage the ozone layer around the earth in terms of electromagnetic waves

A

Because the Ozone layer absorbs ultraviolet light, so without it skin cancer rates will increase

47
Q

Give one way radiologist can protect themselves from X-rays and gamma rays

A

Can stand behind a lead screen

48
Q

Give the dangers of all the electromagnetic waves

A

Radio waves—) N/A
Microwaves—) can heat human body tissue
Infrared radiation—) can create create skin burns
Visible light-) N/A
Ultraviolet—) harmful to eyes, increase skin cancer, cause burns and blisters
X-rays—-) can cause cancer
Gamma rays—-) can cause cancer and damage living things

49
Q

Give two dangers of gamma rays

A

Can cause damage to living things and
cause cancer because high levels of energy ionizes cells, thus mutating them

50
Q

Explain why food stays fresher for longer after being exposed to gamma rays

A

Because gamma rays can kill microorganisms

51
Q

State the relationship between luminous objects and light
And non luminous objects and light

A

Luminous objects give out their own light (eg sun or light bulbs)
Non luminous objects only reflect light

52
Q

Explain why you can not see your reflection on a rough surface

A

Boundary is not flat
so the normals will be pointing at different angles for each angle of incidence
thus the angle of reflection will be emitted in different directions

53
Q

What is the normal

A

An imaginary line that is perpendicular to the surface at point of incidence (where the wave hits the boundary)

54
Q

Give two conditions for total internal reflection to occur

A

When angle of incidence is greater than the critical angle
When light travels from more dense to less dense medium

55
Q

What are the conditions for refraction to occur

A

When rays travel through different mediums,
Cussing the speed to change, causing the direction to change

56
Q

What are the conditions for reflection to occur

A

When light hits an even surface

57
Q

Give the refractive index of glass and of water

A

Glass = 1.5
Water = 1.3

58
Q

Give the refractive index equation

A

n= sin i/sin r

59
Q

Give the equation for wave speed

A

V(m/s) = f(hz) x lambda (m)
Or V= 1/T x lambda

(Same things because another way to write frequency is 1/T

60
Q

Explain what happens to light as it travels from less dense to more dense medium

A

Light slows down
So wavelength decreases as long as frequency is the same
And direction changes, bending closer to the normal
And so angle of incidence is greater than angle of refraction

61
Q

When light travels from less dense to more dense medium, state what happens to the direction in terms of from the Normal

A

Bends towards the normal

62
Q

When light travels from more dense to less dense medium, state what happens to the direction in terms of from the Normal

A

Bends away from the normal

63
Q

Explain what happens to light when it travels from a more dense medium to a less dense medium

(In terms of speed, direction, the normal, wavelength)

A

Light rays speed up
And direction changes, moving further away from the normal
And wavelength
So angle of incidence is smaller than angle of refraction

64
Q

In an experiment to investigate the refraction, explain why your results may be inaccurate?

A

Because the width of the light ray you are using makes it difficult to locate where the centre of it is

(Thus the crosses you make may not be accurate)

65
Q

Explain why the angle of incidence and angle of reflection is the same for both Perspex and glass

A

Because the angle of incidence and angle of reflection is not affected by the medium

66
Q

Explain how the angle of refraction going through glass and through Perspex will differ or be the same and why

A

Angle of refraction will be different for each
Because angle of refraction is affected by the type of material

67
Q

Give six steps to calculate the refractive index of a glass block

A

1)place a light box onto piece of paper with one slit in it, and direct the ray through the glass block so that it comes out on the opposite side
2)draw around the glass block and draw crosses over the light rays
3)remove the glass box and connect the light rays where the light entered the box and when it leaves the box
4)draw the normals
5) measure the angle of incidence and angle of refraction
6)use the equation n= sin i/sin r to calculate the refractive index

68
Q

What is the critical angle

A

The smallest angle of incidence, at which light rays are totally internally reflected

(Ur textbooks definition )

69
Q

What is the critical angle of glass?

A

42 degrees

70
Q

Explain how total internal reflection takes place in a prismatic prism

A

1) light enters at 90 so does not change direction. So light is undifferentiated
2)light passes through the next surface at 45 degrees and because critical angle of glass is 42 degrees, total internal reflection is able to happen
3)so light rays pass straight down to next prism and enters at 90 and does not change direction again
3) enters next surface at 45 degrees again so that total internal reflection can happen again so the ray leaves parallel to the original direction it was going in

71
Q

Explain why optical fibers are better to use in telecommunication than copper wires

A

Have a thinner diameter
so more fibers can be bunched together to carry more signals,
so less energy is lost

72
Q

Explain how optical fibers are used in telecommunication

A

Telephone sends electrical signals which are converted into light energy signals
produced by a laser
across bundles of optical fibers
Which travel to a detector in the telephone receiver
, changing the light signals into electrical signals

73
Q

Give two examples of where optical fibers are used

A

Endoscopes or telecommunication

74
Q

Give five examples of where total internal reflection is used

A

Endoscopes
Telecommunication
Periscope
Binocular
Bike reflectors

75
Q

Explain how total internal reflection happens in binoculars

A

Light enters through lens into a prism
Which refracts the light
Then light is totally internally reflected into the next prism
Then light is refracted again
And then totally internally reflected again into the eye piece

76
Q

Explain how total internal reflection occurs in endoscopes

A

Endoscopes have a low refractive index on the outside, and a high refractive index on the inside.
It contains bunches of optical fibers, through which light from the light source enters
And because it enters at an angle greater than the critical angle, it is able to totally internally reflect
This light reaches the are of the Body
And the light then travels back to the eye piece through another bunch of optical fibers through total internal reflection

77
Q

Give a danger of visible light

A

If bright enough then can cause damage to eyes

78
Q

Refractive index for diamond is 2.4
Refractive index for opal is 1.5
Which will be more sparkly? Explain why

A

Diamond
Because it has a higher refractive index thus a smaller critical angle
This means that there is a larger range of values for which total internal reflection can occur
So if more total internal reflection, then it will sparkle more

(Remember that the minimum angle that TIR can occur is the critical angle. So at any angle that is above the critical angle TIR will occur)

79
Q

How do we hear?

A

Sound waves are longitudinal
So when entering the ear they cause the ear drum to vibrate
The vibrations are turned into electrical signals which we interpret

80
Q

Describe an experiment to measure the speed of sound in air

A

1)You and your friend stand 100m apart from each other and measure this using a trundle wheel
2)Your friend will clap two pieces of wood together, 3)and you will start stop watch when you see them clap it, and will stop stopwatch when you hear the sound
4) repeat at least three times for a certain distance, then change distance and repeat
5)use the equation speed = distance / time and then
calculate an average

81
Q

Describe an experiment to calculate the speed of light in air

A

1)you and your friend should stand 100M away form each other and measure DISTANCE using a TRUNDLE WHEEL
2)friend will clap, and start timer when you see her bang two pieces of wood together and stop when you hear the sound
3)repeat three times for a certain distances and then repeat for different distances
4)use equation speed = distance/time and calculate an average

82
Q

Explain why radio waves are used in broadcasting communication

A

Because they can be reflected from the earths surface

83
Q

Explain why microwaves are used for satellite communication

A

Because they can penetrate the earths surface

84
Q

Explain why visible light is used for fiber optic communication

A

Because it can undergo total internal reflection

85
Q

Explain X-rays are used for medical imaging of bones

A

Because they can penetrate soft tissue but not bones

86
Q

Explain why gamma rays are used for sterilzing medical equipment

A

Because they can kill bacteria

87
Q

a student sitting on the shore of a lake watching ripples on the
surface of the water moving past a toy boat. Explain how he can measure the frequency of the ripples

A

Count the number of waves that pass a point in a specific time, eg ten seconds
Then use the equation F =number of waves/ time period

88
Q

Give 2 properties of sound waves

A

All longitudinal waves
Can not travel though a vaccum bc no particles

89
Q

Which medium do sound waves travel fastest in and why

A

Because particles are closest together so vibrations will be fastest

90
Q

Explain how tempeture can affect a sound wave

A

Temperature can increase or decrease the speed of the sound wave, therefore changing its direction
(So it can be refracted)

91
Q

Which types of waves can be refracted

A

All types
(Both longitudinal and transverse)

92
Q

When a wave slows down, what happens to its wave length and why

A

Wave length also decreases,
Because wave speed and wave length are directly proportional (assuming frequency remains the same)

93
Q

For a graph to show the relationship between critical angle and refractive index, give two reasons why the groah does not start at 0

A

1) a reduced scale, allow morw of the graph to fill the grid, thus showing the trend line more clearly
2)refractive index must always be larger than 1

physics (10 decks)

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