Physics > Waves Yr9 > Flashcards

Waves Yr9 Flashcards

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1
Q

What is wavelength?

A

Distance from 1 peak to the next

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2
Q

What is frequency?

A

How many complete waves there are per second
Hertz (Hz)

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3
Q

1Hz = …?

A

1 wave per second

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4
Q

What is amplitude?

A

Height of the wave (from crest to rest, rest to trough)

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5
Q

What is speed?

A

How fast the wave goes
V

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6
Q

What is period?

A

Time taken (in s) for 1 complete waves to pass a point
T

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7
Q

What is a transverse wave?

A

Oscillations are perpendicular to the direction of energy transfer

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8
Q

What are examples of transverse waves?

A

EM waves
Slinky moving up + down
Waves on strings
Ripples on water

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9
Q

What is a longitudinal wave?

A

Oscillations are parallel to the direction of energy transfer

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10
Q

What are examples of longitudinal waves?

A

Sound + ultrasound
Shockwaves
- some seismic waves
Slinky when you push the end

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11
Q

What do waves carry and transfer?

A

Energy (without transferring matter)

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12
Q

What is a wavefront?

A

Imaginary planes that cut across all the waves, connecting the points on adjacent waves which are vibrating together

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13
Q

What is the distance between each wavefront equal to?

A

1 wavelength

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14
Q

Why does the wave speed catch up to the waves in front of it?

A

Wavefronts bunch up in front of the moving source + spread out behind it

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15
Q

The faster the wave is moving away from you, the …?

A

Longer its wavelength

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16
Q

What happens if a car is moving towards you (Doppler effect)?

A

Frequency of wave increases
Wavelength will be shorter than the wave produced by the source

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17
Q

What happens if a car is moving away from you (doppler effect)?

A

Frequency of wave decreases
Wavelength will be longer than wave produced by the source

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18
Q

What is the order in the electromagnetic spectrum?

A

Radio waves
Microwaves
Infrared
Visible light
Ultraviolet
X-rays
Gamma rays

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19
Q

What is the order of EM waves in order of?

A

Increasing frequency
Decreasing wavelength

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20
Q

What do EM waves travel the same speed in?

A

Free space (vacuum)

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21
Q

What are radio waves used for?

A

Communication

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22
Q

How do long-wave radios work?

A

Transmitted long distances
Long wavelength bend around curved surface of earth

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23
Q

How do short-wave radios work?

A

Received at long distances from the transmitter
Reflected from ionosphere

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24
Q

How do very short-wave radios work?

A

Must be in direct sight of transmitter to get reception
Used for TV, FM radio

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25
What are microwaves used for?
Satellite communication Heating food
26
How are microwaves used in satellite communication?
Signal from transmitter is transmitted into space Picked up by satellite receiver dish Satellite transmits signal back to each - received by a diff satellite dish Mobile phone calls travel as microwaves to nearest transmitter
27
How are microwaves used to heat food?
Microwaves are absorbed by water molecules in food - penetrate few cm before being absorbed Energy is conducted/convected to other parts of food
28
What is infrared radiation used for?
Heating/monitoring temperature
29
How is infrared radiation used for heating?
Electrical heaters radiate IR to keep us warm Grills to cook food
30
How is infrared radiation used in night-vision equipment?
Detects IR given out by objects Turns it into electrical signal - displayed on screen as picture - allows us to see hidden things
31
What is visible light used for?
Optical fibres (communication) Photography
32
How is visible light used in optical fibres?
Carries data over long distances as pulses of light Enters fibre at certain angle Constantly reflects off sides of narrow core Emerges at other end TOTAL INTERNAL REFLECTION
33
What are optical fibres used for?
Telephone Broadband internet cables ‘See inside’ someone
34
How is visible light used in photography?
Camera uses lens to focus VL onto light-sensitive film/sensor Vary aperture, shutter speed, sensitivity of film/sensor to capture a little/lots of light in picture
35
What does the lens aperture do?
Controls how much light enters camera
36
What does the shutter speed do?
Determined how long film/sensor is exposed to light
37
What is ultraviolet used for?
Fluorescent lamps
38
How is ultraviolet used in fluorescent lamps?
UV is absorbed by phosphor coating —> visible light is emitted Energy efficient
39
What are x-rays used for?
Viewing internal structures
40
How are x-rays used to view internal structures?
Fired through body onto detector plate Absorbed by dense materials (bones) - brighter as fewer rays get through Pass through flesh
41
What can exposure to x-rays do?
Cause mutations —> cancer
42
What are safety precautions when using x-rays?
Wear lead aprons + shield Exposure is kept to a minimum
43
What are gamma rays used for?
Sterilisation
44
How are gamma rays used to sterilise medical equipment and food?
Kills the microbes
45
Why is it better to use gamma rays to sterilise medical equipment?
Plastic instruments get damaged at high temperatures
46
Why is it good to sterilise food?
Kills microbes Keeps food fresh for longer
47
Why can microwaves be dangerous?
Similar frequency to vibrations of molecules - increases these vibrations - INTERNAL HEATING
48
What are safety precautions for using microwaves?
Microwave ovens need shielding - stop them from reaching user
49
Why can infrared radiation be dangerous?
Frequency makes surface molecules vibrate - SKIN BURNS
50
Why are safety precautions for using infrared radiation?
Use insulating materials - reduces IR reaching ur skin
51
Why can ultraviolet radiation be dangerous?
Some frequencies are ionising - DAMAGE SURFACE CELLS, BLINDNESS, CANCER
52
What does ionising mean?
Carries enough energy to knock electrons off atoms
53
What are safety precautions for using ultraviolet?
Wear sunscreen w UV filters Stay out of strong sunlight
54
Why can gamma radiation be dangerous?
Ionising - carries a lot of energy Can penetrate further into body - CELL MUTATION/DESTRUCTION —> TISSUE DAMAGE/CANCER
55
What are safety precautions for using gamma radiation?
Keep in lead-lined box Exposure is kept to a minimum
56
What is diffuse reflection?
Light reflects from an uneven surface (paper) - light reflects at diff angles
57
What is clear reflection?
Light reflects from an even surface (mirror) - light reflects at same angle
58
Angle of incidence = …?
ANGLE OF REFLECTION
59
What do waves travel at different speeds in?
Substances w diff densities
60
EM waves travel slower in …?
DENSER materials
61
Sound waves travel faster in …?
DENSER materials
62
What happens if waves pass to a more dense medium?
Bend TOWARDS the normal - slows down - angle of refraction is SMALLER than angle of incidence
63
What happens if waves pass to a less dense medium?
Bend AWAY from normal - speeds up - angle of refraction is LARGER than angle of incidence
64
What do triangular prisms do to light?
Disperse white light
65
What do different wavelengths of visible light do?
Refract by different amounts
66
What does refractive index mean?
How fast light travels in that material
67
The higher the refractive index, the …?
LOWER the critical angle
68
How do you find the refractive index of glass?
1) draw around glass block, direct a ray of light through it at an angle, trace incident + emergent ray, remove block, draw refracted ray 2) draw in normal at 90 to edge of block, at point where ray enters block 3) use a protractor to measure angle of incidence + refraction 4) calculate refractive index using equation
69
What happens to the angle of refraction if you increase the angle of incidence?
Gets closer to 90
70
How do you use a semicircular block to show total internal reflection?
1) incident light ray is aimed at curved edge of block - enters at right angle to edge 2) mark positions of rays + block on paper, use protractor to measure i and r for diff angles of incidence
71
What is the critical angle?
The angle of incidence when the angle of refraction is 90 degrees
72
What does refraction mean?
When light bends as it passes from 1 medium to another
73
What are the 2 criteria for total internal reflection?
1) rays of light must travel from a MORE dense to a LESS dense medium 2) angle of incidence must be GREATER than critical angle
74
What happens when the angle of incidence is LESS than the critical angle?
Light is refracted AWAY from normal
75
What happens when the angle of incidence is EQUAL to the critical angle?
Light is refracted at 90 to normal Travels along surface of denser medium
76
What happens when the angle of incidence is GREATER than the critical angle?
No refraction TOTAL INTERNAL REFLECTION - all light is reflected
77
How are optical fibres used for total internal reflection?
Core of fibre is narrow so light passes through hitting core-cladding boundary at angles higher than C - always totally internally reflected
78
When does TIR stop working in optical fibres?
If fibre is bent too sharply
79
What 2 materials can optical fibres be made of?
Glass Plastic
80
How are prisms used in total internal reflection?
PERISCOPE: Ray of light travels into 1 prism - TIR by 90 Travels through another lower down - TIR by 90 Ray now travels parallel to its initial path at diff height
81
What do prisms using TIR do?
Allow us to see objects that aren’t in our direct line of sight
82
What are sound waves caused by?
Vibrating objects
83
How do sound waves pass through surrounding mediums?
As a series of compressions
84
What are sound waves reflected by?
Hard flat surfaces
85
What are sound waves absorbed by?
Carpets Curtains
86
How do sound waves become refracted?
When entering different mediums
87
What happens if a sound waves travels into a denser medium?
SPEEDS up
88
Why is refraction in sound waves (change in direction) hard to see?
They are always spreading out
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