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physics > waves (paper 2) > Flashcards

waves (paper 2) Flashcards

1
Q

what do waves do

A

transfer energy in the direction they are travelling

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2
Q

describe transverse waves

A

the vibrations are perpendicular to the direction of energy transfer

a spring wiggled from side to side gives a transverse wave

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3
Q

describe a longitudinal wave

A

the vibrations are parallel to the direction of energy transfer

if you push the end of a spring, you get a longitudinal wave

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4
Q

examples of transverse waves

A

all electromagnetic waves

ripples in water

a wave on a string

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5
Q

examples of longitudinal waves

A

shock waves

ultrasound

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6
Q

what is the amplitude of a wave

A

the maximum displacement of a point on a wave away from its undisturbed position.

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7
Q

what is the wavelength of a wave

A

the distance from a point on one wave to the equivalent point on the adjacent wave.

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8
Q

what is the frequency of a wave

A

the number of waves passing a point each second

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9
Q

describe a method to measure the speed of sound waves in air

A

by attaching a signal generator to a speaker you can generate sounds with a specific frequency

set up the oscilloscope so the detected waves at each microphone are shown as separate waves

start with both microphones next to the speaker, then slowly mov one away until the two waves are aligned on the display, but has moved exactly one wavelength apart

measure the distance between the microphones to find one wavelength

you can then use the wave speed formula to find the speed of the sound waves passing through the air - the frequency is whatever you set the signal generator to

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10
Q

describe a method to measure the speed of ripples on a water surface.

A

using a signal generator attached to the dipper of a ripple tank, you can create water waves at a set frequency

dim the lights and turn on the lamp - you will see a wave pattern made by the shadows of the wave crests on screen below the tank

the distance between each shadow line is equal to one wavelength. Measure the distance between the shadow lines that are 10 wavelengths apart, then divide the distance by 10 to find the average wavelength. this is a suitable method for measuring small wavelengths

use wave speed equation to calculate the speed of the waves

this set up is suitable for investigating waves, because it allows you to measure the wavelength without disturbing the waves

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11
Q

method for the wave on a spring practical

A

in this practical you create a wave on a string - you use a signal generator, and attach it to a vibration transducer which converts the signals to vibrations

set up the signal generator, vibration transducer, the string, the bench, the pulley and the masses

then turn on the signal generator and vibration transducer and the string will start to vibrate

you can adjust the frequency setting on the signal generator to change the wavelength. The frequency you need will depend on the length of the string between the pulley and the transducer and the masses you have used

the best way to measure the wavelength accurately is to measure the length of all the half wavelengths then work out a mean value for the half wavelength, and then double the value to get the full wavelength

the frequency of the wave is whatever the signal generator is set to

you can find the speed of the wave using the wave speed equation

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12
Q

what can happen when waves arrive at boundary between two different materials

A

1 - waves are absorbed by the material

2 - waves are transmitted - they carry on travelling

3 - waves are reflected

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13
Q

when does specular reflection happen

A

when a wave is reflected in a single direction by a smooth surface e.g. when light is reflected by a mirror you get a nice clear reflection

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14
Q

when does diffuse reflection happen

A

when a wave is reflected by a rough surface and the reflected rays are scattered in lots of different directions

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15
Q

why does diffuse reflection happen

A

because the normal is different for each incoming ray, which means the angle of incidence is different for each ray

the rule of angle of incidence = angle of reflection still applies

when light is reflected by a rough surface, the surface appears matte and you don’t get a clear reflection of objects

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16
Q

what is refraction

A

when a wave crosses a boundary between materials at an angle, it changes direction - it is refracted

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17
Q

what does how much something is refracted by depending on

A

the density of the two materials - usually the higher density a material, the slower a wave travels through it

how much the wave speeds up or slows down

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18
Q

what changes and what stays the same as a wave is refracted

A

the wavelength changes

BUT the frequency stays the same

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19
Q

what is the optical density of a material

A

a measure of how quickly light can travel through it - the higher the optical density, the slower light waves travel through it

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20
Q

method for investigating refraction through transparent materials

A

place a transparent rectangular block on a piece of paper and trace around it, use a ray box or a laser to shine a ray of light at the middle of one side of the block

trace the incident ray and mark where the light ray emerges on the other side of the block

remove the block and with a straight line, join up the incident ray and the emerging point to show the path of the refracted ray through the block

draw the normal at the pint where the light ray entered the block, use a protractor to measure the angle between the incident ray and the normal and the angle between the refracted ray and the normal

repeat this experiment using rectangular blocks made from different materials, keeping the incident angle the same throughout

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21
Q

method for how light reflects differently depending on the smoothness of a surface

A

take a piece of paper and draw a straight line across it

place an object so one of its side lines up with this line

shine a ray of light at the objects surface and trace the incoming and reflected light beams

draw the normal at the point where the ray hits the object, use a protractor to measure the angle of incidence and the angle of reflection and record these values in a table

also make a note of the width and brightness of the reflected light ray

repeat these steps for a range of objects

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22
Q

how do sound waves cause us to hear sound

A

sound waves cause the ear drum and other parts to vibrate which causes the sensation of sound.

The conversion of sound waves to vibrations of solids works over a limited frequency range.

This restricts the limits of human hearing.

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23
Q

what types of waves do all electromagnetic waves have in common and what similarities do they share

A

they are transverse waves and they all travel at the same speed through air or a vacuum

24
Q

pattern in the electromagnetic spectrum

A

it increases in frequency and decreases in wavelength

25
Q

uses of radio waves

A

communication

radio signals

bluetooth

TV and FM radio transmissions

26
Q

uses of microwaves

A

communications to and from satellites

microwave ovens - heat up water molecules

27
Q

uses of infrared radiation

A

infrared cameras - can monitor temperature and detect infrared radiation

food can be cooked IR radiation

electric heaters

28
Q

how do fiber optic cables use visible light to transmit data

A

optical fibres are thin glass or plastic fibres that can carry data over long distances as pulses of visible light

they work because of reflection, the light rays are bounced back and forth until they reach the end of the fiber

light is not easily absorbed or scattered as it travels along a fiber

29
Q

uses of ultraviolet radiation

A

fluorescent lights

security pens

gives people a suntan

tanning beds

30
Q

uses of X-rays

A

X-ray photographs

can treat cancer

31
Q

uses of gamma rays

A

radiotherapy

medical tracers

32
Q

precautions doctors take against gamma rays and X-rays

A

radiographers wear lead aprons and stand behind a lead screen or leave the room to keep exposure to a minimum

33
Q

how can some electromagnetic ne harmful to people

A

high frequency waves e.g. gamma all transfer lots of energy that can cause lots of damage

UV radiation damages surface cells, causes sun burn and increases risk for skin cancer

X-rays and gamma rays are ionising radiation so they can cause gene mutation and cancer

34
Q

what is radiation dose measured in

A

sieverts - a measure of risk of harm from the body being exposed to radiation

35
Q

key facts about a convex lens

A

it bulges outwards - it causes the the rays of light parallel to the axis to be brought together at the principal focus

36
Q

key facts about concave lens

A

caves inwards - it causes rays of light parallel to the axis to spread out

37
Q

where is the principal focus of a convex lens

A

where rays hitting the lens parallel to the axis all meet

38
Q

where is the principal focus of a concave lens

A

the point where the rays hitting the lens parallel to the axis appear to all come from - you can trace them back until they all appear to meet up at a point behind the lens

39
Q

what is the focal length

A

the distance from the center of the lens to the principal focus

40
Q

what are the three rules for refraction in a convex lens

A

1 - the incident ray parallel to the axis refracts through the lens and passes through the principle focus on the other side

2 - an incident ray passing through the principal focus refracts through the lens and travels parallel to the axis

3 - an incident ray passing through the centre of the lens carries on in the same direction

41
Q

what are the three rules for refraction in a concave lens

A

1 - an incident ray parallel to the axis refracts through the lens, and travels in line with the principal focus

2 - an incident ray passing through the lens towards the principal focus refracts through the lens and travels parallel to the axis

3 - an incident ray passing through the centre of the lens carries on in the same direction

42
Q

what is a real image

A

where the light from an object comes together to form an image on a ‘screen’ - like the image formed on the eyes retina - the ‘screen’ at the back of the eye

43
Q

what is a virtual image

A

when the rays are diverging , so the light from the object appears to be coming from a completely different place

44
Q

to describe an image properly what are the three things you have to say

A
  • how big it is compared to the object
  • whether it is upright or inverted relative to the object
  • whether it is real or virtual
45
Q

what do opaque objects do

A

they do not transmit light

when visible light waves hit them, they absorb some wavelength of light and reflect others

46
Q

what do white objects do

A

reflect all of the wavelengths of visible light equally

47
Q

what do black objects do

A

absorb all wavelengths of visible light

your eyes see black as a lack of any visible light

48
Q

what do colour filters do

A

used to filter out different wavelengths of light so that only certain colours are transmitted

49
Q

method for investigating absorption with the melting wax trick

A

set up the two sets of wax and ball bearing, silver slide, matt black slide and identical metal plates

two ball bearings are each stuck to one side of a metal plate with solid pieces of candle wax, the other sides of these plates are then faced towards the flame. the plates are placed the same distance away from the flame

the sides of the plates that are facing towards the flame each have a different surface colour - one is matte black and the other is silver

the ball bearing on the black plate will fall first as the black surface absorbs more infrared radiation - transferring more energy to the thermal energy store of the wax. This means the wax on the black plate melts before the wax on the silver plate

50
Q

method for investigating emission with a leslie cube

A

place an empty Leslie cube on a heat proof mat

boil water in a kettle and fill the Leslie cube with boiling water

wait for the cube to warm up, then hold a thermometer against each of the four vertical faces pf the cube, you should find that all the faces of the cube are the same temperature

hold a infrared detector a set distance away from one of the cubes vertical faces and record the amount of IR radiation it detects

repeat this for the other faces of the cube

you should find that you detect more IR radiation from the black surface than the white one

you should repeat the experiment more than once to make sure your results are reliable

51
Q

what is a perfect black body

A

an object that absorbs all the radiation that hits it, no radiation is reflected or transmitted

52
Q

what range can humans hear from

A

20Hz - 20kHz

53
Q

what are ultrasound waves

A

sound with frequencies higher than 20,000 Hz

54
Q

uses of ultrasound

A

prenatal scanning

used to find flaws in objects such as pipes or materials such as wood or metal

55
Q

P - waves key facts

A

they can travel through earths core

they are longitudinal

they travel through solids and liquids

they travel faster than S - waves

56
Q

S - waves key facts

A

S - waves cannot travel through the earths core

S - waves are transverse

they cant travel through liquids or gases

they are slower than P - waves

physics (8 decks)

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