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physics > P5 WAVES IN MATTER > Flashcards

P5 WAVES IN MATTER Flashcards

1
Q

what’s the formula for wave speed?

A

wave speed= frequency x wavelength

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2
Q

what is wavelength?

A

the length of a full cycle of a wave

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3
Q

what is frequency?

A

the number of waves passing a point per sec

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4
Q

what are the differences between transverse and longitudinal waves?

A

in transverse waves, the vibrations are at right angles to the direction of wave travel whereas in longitudinal waves, the vibrations are parallel to the direction of wave travel.

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5
Q

what stays the same when waves cross a boundary?

A

frequency

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6
Q

what happens to wavelength when a wave slows down/speeds up?

A

decreases when slows, increases when speeds up

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7
Q

how does a wave bend when it slows down/speeds up?

A

bends towards the normal when it slows down and bends away from the normal when it speeds up

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8
Q

why is ultrasound useful?

A

it can pass through the body but is partially reflected at boundaries between dif tissues

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9
Q

why does ultrasound work?

A

if you know the speed of ultrasound in different tissues, you can calculate the distance to different boundaries and produce an image

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10
Q

how does sonar work?

A

you can find distances using the time taken for an echo to return and the speed of sound in water

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11
Q

how are we able to hear and understand?

A

the outer ear gathers a sound wave and directs it to the eardrum. the eardrum vibrates, causing the ossicles to vibrate. these ossicles amplify the vibration and pass it onto the inner ear through the oval window. the cochlea contains fluid which transmits the movements of the oval window to small hairs in the cochlea. these hairs are attached to sound detecting cells that release chemical substances, which makes nerves send a signal down the auditory nerve to the brain. the brain processes the signal and you hear the sound

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12
Q

what’s the frequency range humans can hear?

A

20-20,000Hz

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13
Q

why does hearing change due to aging?

A

as you get older, you lose shorter hairs in the cochlea so it is harder to hear higher frequencies. also, upper limit increases and sounds need to be louder to be heard

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14
Q

describe how ripples on water surfaces are used to model transverse waves

A

ripples form on water: the oscillation of the waves is perpendicular to the direction of travel, modelling transverse waves

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15
Q

what type of wave are sound waves?

A

longitudinal

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16
Q

how can you measure the speed of a transverse wave using a ripple tank?

A

use a lamp and motor to adjust the speed. you can count the number of waves passing a point in 10 secs then divide by 10 to find frequency. you measure wavelength by measuring the length of a number of waves and dividing by how many there are.

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17
Q

how can you measure the speed of a sound wave?

A

gather 2 microphones, an oscilloscope, loudspeaker and signal generator. attach the loudspeaker to the signal generator and note its frequency. attach each mic to the oscilloscope to see the trace of the wave on the screen. separate the microphones so they appear as 2 separate waves on the oscilloscope. then align the wavelengths by slowly moving the mics away from each other. now measure the distance between the mics (wavelength). use formula.

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18
Q

how can we tell that the wave travels and the water doesn’t move in a ripple tank?

A

when a ball is placed on the surface of a pond and ripples move across it, the ball moves up and down but not outwards with the water

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19
Q

how can we tell that it is the sound waves travelling and not air?

A

eg a loudspeaker doesn’t produce a gust of wind when used

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20
Q

what type of waves are EM?

A

transverse

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21
Q

what velocity do EM waves have in space?

A

all the same velocity

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22
Q

what are EM waves transferred from?

A

source to absorber

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23
Q

give an example of EM waves transferring energy from source to absorber

A

when you turn an electric heater on, infrared waves transfer energy from the thermal energy store of the heater to your thermal energy store

24
Q

describe the 7 groupings of the EM spectrum from long wavelengths and low frequency to short wavelengths and high frequency

A

radio, micro, infrared, visible, UV, x rays, gamma rays

25
Q

which part of the EM spectrum is the only part that our eyes can detect?

A

visible light

26
Q

what type of wave is light?

A

EM wave

27
Q

name a practical use of radio waves

A

communication eg broadcasting tv/radio

28
Q

name a practical use of microwaves

A

heat up food

29
Q

name a practical use of infrared rays

A

electrical heaters/thermal imaging cameras

30
Q

name a practical use of UV rays

A

radiotherapy

31
Q

name a practical use of xrays

A

kill/damage cancer cells (radiation therapy), detecting fractures in bones

32
Q

how can UV rays have hazardous effects on body tissues?

A

can cause melanoma

33
Q

how can x rays have hazardous effects on body tissues?

A

ionising radiation, can cause mutations and cancer

34
Q

how can gamma rays have hazardous effects on body tissues?

A

ionising radiation, can cause mutations and cancer

35
Q

name a practical use of gamma rays

A

gamma camera + tracers

36
Q

why are we able to use x rays to diagnose conditions like bone fractures?

A

x rays are mostly transmitted by soft tissue but absorbed by denser materials eg bones

37
Q

how does infrared radiation interact with the human body?

A

mostly absorbed/reflected by skin, some heating.

38
Q

how do gamma rays interact with the body?

A

gamma rays pass completely through the human body. transmitted by skin, soft tissue and bone (so radiotracers can be used and detected by a gamma camera)

39
Q

how does ultrasound work?

A

ultrasound passes through skin, muscle and bone but are partially reflected at boundaries between different tissues. if you know the speed of ultrasound at dif tissues, you can calculate the distance to dif boundaries- the reflections are processed by a computer to form an image

40
Q

how can radio waves be produced by/ induce oscillations in circuits?

A

an oscillating pd across a wire makes electrons move back and forth, producing a changing electric and magnetic field (a radio wave). when the waves meet another piece of metal, it makes the electrons move and produces an electrical signal

41
Q

what can EM waves do when they meet a boundary?

A

be absorbed, reflected, transmitted or refracted

42
Q

what does the refraction, absorption, transmission or reflection of a wave depend on?

A

wavelength

43
Q

what is long sighted and short sightedness corrected using?

A

long sightedness is corrected with a convex lens, short sightedness is corrected with concave lens

44
Q

how do concave lenses corrected short sightedness?

A

placed in front of the eye to correct short sight, which diverges light before it enters the eye

45
Q

how do convex lenses correct long sightedness?

A

convex lens in front of eye so light converges before it enters the eye

46
Q

what type of image will a concave lens always produce?

A

virtual

47
Q

how do you draw a ray diagram for a concave lens?

A

draw a ray from the top of the object straight across to the lens. draw another ray from the top of the object to the middle of the lens. draw a ray from the principal focus going through the first ray and make it dotted before it reaches the lens. the intersection between the dotted line and the 2nd ray is where the top of the image is. repeat for bottom of image

48
Q

how do you draw a ray diagram for a convex lens?

A

draw a ray from the top of the object across to the lens and stop there. draw another ray from the top of the object through the middle of the lens to the other side. draw a refracted ray passing through f from the first ray. mark where the rays meet (top of image)

49
Q

what is the rule for all reflected waves?

A

angle of incidence = angle of reflection

50
Q

why are some objects opaque?

A

they don’t transmit light

51
Q

what does the colour of an object depend on?

A

the wavelength of light it reflects

52
Q

why are objects white or black?

A

white objects reflect all wavelengths of visible light equally and black objects absorb all wavelengths of visible light

53
Q

what colour does a primary colour filter transmit?

A

only that colour

54
Q

what is specular vs diffuse scattering?

A

specular is reflection from a smooth surface and diffuse is when light is scattered in all direction

55
Q

why are some objects translucent/transparent?

A

they transmit light: they appear to be the colour of light corresponding to the wavelengths most strongly transmitted by the object

physics (8 decks)

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