Topic 6 - Waves Flashcards
what do waves do?
waves transfer energy from one place to another without transferring any matter
what happens when waves travel through a medium?
the particles of the medium oscillate and transfer energy between each other (the particles stay in the same place only energy is transferred)
what is the amplitude of a wave?
the maximum displacement of a point on the wave from its undisturbed position
what is the wavelength?
the distance between the same point on 2 adjacent waves (between 2 peaks)
what is frequency?
the number of complete waves passing a certain point per second
what is frequency measured in?
hertz (Hz) which is the number of waves per second
what is the period of a wave?
the amount of time it takes for a full cycle of the wave
what is the equation to find the period of a wave?
. <u> 1</u>
T= f
all waves are either…………….. or ………………….
transverse or longitudinal
what are transverse waves?
where the oscillations are perpendicular to the direction of energy transfer.
e.g. electromagnetic waves, ripples in water and waves on string
what are longitudinal waves?
where oscillations are parallel to the direction of energy transfer.
e.g. sound waves, ultrasound and shock waves
what is the wave speed?
the speed at which energy is being transferred(or the speed the wave is moving at)
what is the equation for wave speed?
v=fλ
what is v?
wave speed (m/s)
what is f?
frequency(Hz)
what is λ?
wavelength (m)
what is T?
period (s)
How can you generate sounds with a specific frequency?
by attaching a signal generator to a speaker. you can use 2 microphones and an oscilloscope to find the wavelength of the sound waves generated
how can you set up an experiment to measure the speed of sound?
- set up the oscilloscope so the waves detected at each microphone are shown as separate waves
- start with both microphones next to the speaker but move 1 until the 2 waves are aligned on the display but are a wavelength apart
- measure distance between microphones to find wavelength
how to find the speed of sound after conducting an experiment?
use the formula to find speed using wavelength and frequency.
the frequency is whatever you set the signal generator to
what is the speed of sound in air?
330 m/s
How can you create water waves at a set frequency?
using a signal generator attached to the dipper of a ripple tank
how can you see waves crest on a screen?
use a lamp to project the shadow of the wave crests on a screen below the tank. make sure the size of the waves shadows are the same as the actual wave
how do you conduct an experiment to measure the speed of water ripples?
- the distance between each shadow line of a wave crest is equal to one wave length. you can find the average wave length by measuring 10 wavelengths worth of distance between the lines and dividing it by 10. (you can take a picture of the screen with a ruler next to it to do this)
- find the speed using the frequency on the signal generator
Why is projecting waves onto a screen a suitable way for investigating waves?
it allows you to measure wavelength without disturbing the waves
how to set up an investigation for measuring waves on strings?
attach a signal generator to a vibration transducer. a string should be strung between the vibration transducer and a pulley and have weights attached to the end to pull the string taught.
how to conduct an experiment for measuring waves on strings?
turn on the signal generator and vibration transducer, so the string starts vibrating. adjust the frequency so there’s a clear wave on the string.
then measure the wavelength (you can do this by creating a few half - wavelengths on the string and measure the length of the string and divide it by the number of waves then multiply it bu 2)
the frequency is what is on the signal generator.
the speed can then be calculated
what can happen when a wave arrives at a boundary between 2 different materials?
it is absorbed
it is transmitted
it is reflected
what happens when a wave is absorbed?
when a wave is absorbed by the material the wave is trying to cross into - this transfers energy to the material’s energy stores
what happens when a wave is transmitted?
the waves carry on travelling through the new material. this often leads to refraction
what determines what happens when a wave hits a material?
it depends on the wavelength of the wave and the properties of the materials involved
what is the angle of incidence?
the angle between the incoming wave and the normal
what is the angle of reflection?
the angle between the reflected wave and the normal
what is the normal?
an imaginary line that’s perpendicular to the surface at the point of incidence. this is usually shown as a dotted line
what is specular reflection?
when a wave is reflected in a single direction by a smooth surface. e.g. light reflected in a mirror gives a clear reflection
what is diffuse reflection?
when a wave is reflected by a rough surface and the reflected rays are scattered in lots of different directions. when light is reflected by a rough surface, the surface appears matte, not shiny so it doesn’t have a clear reflection
why does diffuse reflection happen?
because the normal is different for each incoming ray, which means that the angle of incidence is different for each ray.
what are electromagnetic waves?
they’re all transverse waves, that transfer energy from a source to an absorber. they all travel at the same speed through air or a vacuum.
what do electromagnetic waves form?
they form a continuous spectrum over a range of frequencies. they are grouped into 7 basic types based on wavelength and frequency
what are the 7 groups in the electromagnetic spectrum? from longest wavelength to shortest
Radio waves micro waves infrared visible light ultraviolet X-rays gamma rays
why does the electromagnetic spectrum have such a large range of frequencies?
because EM waves are generated by a variety of changes in atoms and their nuclei. e.g. changes in the nucleus of an atom creates gamma rays. this also explains why atoms can absorb a range of frequencies - each one causes a different change.
because of the different properties they are used for different purposes
when is a wave refracted?
when a wave crosses a boundary between materials at an angle it changes direction (this is refraction)
what determines how much a wave refracts?
how much it speeds up or slows down, which usually depends on the density of the 2 materials (higher density = slower the wave travels through)
which way will a wave refract?
if a wave slows down when it crosses a boundary it will bend towards the normal. if it speeds up it bends away from the normal
what changes when a wave crosses a boundary?
its wavelength changes but its frequency does not. if the wave travels along the normal it will change speed but not refract
what is the optical density of a material?
its a measure of how quickly light can travel through it - the higher the optical density, the slower light waves travels through it
how to construct a ray diagram for a refracted ray:
- draw a boundary between 2 materials and a normal perpendicular to this.
- draw incident ray that meets normal at boundary, draw angle of incidence with protractor if angle is given
- draw refracted ray on other side of boundary line (draw it closer to the normal if 2nd material is optically denser and the angle of refraction is smaller if it is less dense the angle of refraction is bigger and the refracted ray bends away form the normal)
where should you conduct light investigations?
in a dim room so you can clearly see the light rays.
what should you use to produce light in an investigation about investigating light?
either a ray box or a laser to produce thin rays of light, this is so you can easily see the middle of the ray when tracing and measuring angles from it
how to conduct an investigation for refraction:
- place a transparent block on a piece of paper and trace around it, shine a ray of light at the block
- trace the incident ray and the ray coming out the other side, then draw a line between the these 2 lines inside the drawing of the block to show the path of the refracted ray through the block
- draw the normal, then use a protractor to find the angle of incidence and the angle of refraction
- repeat for different objects, it should change
how to conduct an experiment for reflection:
- draw a straight line on a piece of paper and place your reflective object along this line
- shine a ray of light at the object’s surface and trace the incident ray and reflected ray.
- draw the normal and measure the angle of incidence and the angle of reflection, make note of the width and brightness of the reflected ray too
- repeat for different objects, it should change
what kind of reflections do smooth surfaces make?
smooth surfaces give clear reflections(reflected ray as is thin and bright as incident ray).
what kind of reflections do rough surfaces make?
rough surfaces cause diffuse reflection, so the reflected ray is wider and dimmer.
what are electromagnetic waves made up of?
oscillating electric and magnetic fields
what frequency are radio waves?
1m - 10 ^4 m
what frequency are micro waves?
10 ^-2 m
what frequency are infrared?
10 ^-5 m
what wavelength is visible light?
10 ^-7 m
what frequency are ultra violet?
10 ^-8 m
what frequency are X - rays?
10 ^-10 m
what frequency are gamma rays?
10 ^-15 m
what are alternating currents made of?
they are made up of oscillating charges. as the charges oscillate, they produce oscillating electric and magnetic fields. the frequency of the waves produced will be equal to the frequency of the alternating current.
how can you produce radio waves?
using an alternating current in an electrical circuit.
what are transmitters?
the object in which charges oscillate to create radio waves
what happens when transmitted radio waves reach a receiver?
the radio waves are absorbed. this energy carried by the waves is transferred to
the electrons in the material of the receiver. this energy causes electrons to oscillate and if the receiver is part of a complete electrical circuit, an ac current is produced with the same frequency as the radio waves that generated it
what are radio waves?
electromagnetic radiation with wavelengths longer than 10cm.
what are long-wave radio waves?
(wavelengths of 1-10km) travel far distances because they diffract around the curved surface of the world, around hills, through tunnels and more. so radio signals can be received even if the transmitter is not in line of sight of the receiver
what are short-wave radio signals?
(wavelengths of 10m - 100m) they can be received at long distances from transmitter because they are reflected from the ionosphere
what is the ionosphere?
an electrically charged layer in the earths upper atmosphere
what can short wave radio waves be used for?
Bluetooth uses them to send data over short distances between devices without wires.
tv and fm radio transmissions have very short wavelengths
what are medium-wave signals?
they can also reflect from the ionosphere, depending on atmospheric conditions and the time of day
what kind of radiation does communication to and from satellites use?
microwaves, its best to use microwaves that can pass easily through the earths atmosphere
how are signals transmitted for satellite Tv?
the signal from a transmitter is transmitted into space and picked up by the satellite receiver dish orbiting the earth. the satellite transmits the signal back to earth and its received by a satellite dish on the ground. there is a slight time delay because of the long distance the signal has to travel
how do microwave ovens work?
the microwaves penetrate up to a few centimetres into the food before being absorbed by the water molecules in the food, causing them to heat up, this energy is then transferred to the rest of the molecules in the food by heating
where does infrared radiation come from?
its given out by all hot objects, the hotter the object, the more IR radiation it gives out
what can infrared be used for?
infrared cameras can be used to detect infrared radiation and monitor temperature.
it can be used to cook food
electrical heaters can heat a room this way
how do infrared cameras work?
the camera detects the IR radiation and turns it into an electrical signal which is displayed on a screen as a picture, the hotter it is the brighter
how can infrared radiation be used to heat food?
absorbing IR causes objects to get hotter, so food can be cooked using it. the temperature of the food increases when it absorbs IR radiation
how do electrical heaters use infrared?
they contain a long piece of wire that heats up when a current flows through it, this wire emits lots of infrared radiation which is absorbed by objects and the air in the room into the thermal energy stores causing their temperature to increase
what are optical fibres?
thin glass or plastic fibres that can carry data over long distances as pulses of visible light.
how do optical fibres work?
they work because of reflection, the light rays are bounced back and forth until they reach the end of the fibre. light is not easily absorbed or scattered as it travels along a fibre
what is fluorescence?
a property of certain chemicals, where ultraviolet radiation is absorbed and then visible light is emitted
what can ultraviolet radiation be used for?
fluorescent lights
security pens
tanning salons
how can ultraviolet light be used for fluorescent lights?
fluorescent lights generate UV light which is absorbed and re-emitted as visible light by a layer of phosphorus on the inside of the bulb. they are energy-efficient so they’re good to use when light is needed for long periods
how can ultraviolet light be used for security pens?
they can be used to mark property with your name. the ink will glow under UV light but its invisible otherwise
how can ultraviolet light be used for tanning salons?
UV is produced by the sun and exposure to it is called a suntan. in tanning salons uv lamps are used to give them an artificial tan. overexposure can be dangerous
how are X-rays used in hospitals?
radiographers in hospitals use them to take ‘photographs’ and check for broken bones
how do X-Rays work?
they pass easily through flesh but not bone so its the amount of radiation that is absorbed or not that forms the image. the brighter parts of the image is where fewer X-rays get through
how do radiographers use X-rays and gamma rays to treat people for cancer?
high doses of these rays kill all living cells - they are directed towards cancer cells to avoid killing to many healthy cells
how can gamma radiation be used as a medical tracer?
a gamma-emitting source is injected into the patient and its progress is followed through the body. gamma radiation is well suited for this because it can pass out through the body to be detected
what safety precautions are taken with X-rays and gamma rays in hospitals?
they can both be harmful to people, so radiographers wear lead aprons and stand behind a lead screen or leave the room to keep exposure to a minimum
how can x-rays and gamma rays be used in medicine?
x-rays can take photos
both can help treat cancer
gamma can act as a medical tracer
how dangerous are low frequency waves?
they don’t transfer much energy and so mostly pass through soft-tissue without being absorbed e.g. radio waves
how dangerous are high frequency waves?
they all transfer lots of energy and so can cause lots of damage e.g. UV, X-rays and gamma rays
how dangerous is UV radiation?
it damages surface cells which can lead to sunburn and cause skin to age prematurely. some more serious effects are blindness and an increased risk of skin cancer
how dangerous are X-rays and gamma rays?
they are types of ionising radiation, this can cause gene mutation or cell destruction, and cancer
what is radiation dose?
its a measure of the risk of harm from the body being exposed to radiation, its not a measure of the total amount of radiation absorbed. measured in sieverts
what does the risk of radiation depend on?
the total amount of radiation that has been absorbed and how harmful the type of radiation is
how does a CT scan work?
it uses X-rays and a computer to build a picture of the inside of a patients body.
what are the 2 types of lenses?
convex and concave
what is a convex lens?
it bulges out ward. it causes rays of light parallel to the axis to converge at the principal focus
what is a concave lens?
is a lens thats caved inward. it causes parallel rays of light to spread out (diverge)
what is the axis of a lens?
a line passing through the middle of the lens
what is the principal focus of a convex lens?
where rays hitting the lens parallel to the axis meet
what is the principal focus of a concave lens?
where rays hitting the lens parallel to the axis appear to come from. they can be traced back to a point where they appear to meet up behind the lens
what is the focal length?
the distance from the centre of the lens to the principal focus
what are the 3 rules for refraction in a convex lens?
- incident rays parallel to axis refract through the lens and pass through the principal focus on the other side
- incident rays passing through the principal focus refract through the lens and travel parallel to the axis
- incident rays passing through the centre of the lens carry on in the same direction
what are the 3 rules for refraction in a concave lens?
- incident rays parallel to the axis refract through the lens and travel in line with the principal focus
- incident rays passing through the lens towards the principal focus refract through the lens and travel parallel to the axis
- incident rays passing through the centre of the lens carry on in the same direction
what is a real image?
where the light from an object comes together to form an image on a ‘screen’. like the image formed on an eye’s retina
what is a virtual image?
when the rays are diverging, so the light from the object appears to be coming from a completely different place. e.g. your face in a mirror is virtual because it appears to be behind the mirror, or through a magnifying glass it looks a lot bigger
what must you include when describing an image?
how big it is compared to the object
whether it is upright or inverted
whether it is real or virtual
how to draw ray diagrams for a convex lens:
from the top of the object draw 2 lines, 1 parallel to the axis and the other going straight through the middle of the lens
the incident line that is parallel to the axis is refracted through the principal focus on the other side of the lens
where the 2 rays meet is the top of the image
what images are created at different distances from the lens?
F is the principal focus
an object at 2F will create a real, inverted image the same size at 2F
between F and 2F will create a real, inverted image bigger than than the object, beyond 2F
an object nearer than F will make a virtual image, the right way up, bigger than the object on the same side of the lens
how to draw ray diagrams for a concave lens:
from the top of the object draw 2 lines, 1 parallel to the axis and the other going straight through the middle of the lens
the incident ray thats parallel is refracted so it appears its coming from the principal focus
where the 2 rays meet is the top of the image
what kind of image does a concave lens produce?
it is always virtual, the right way up, smaller than the object and on the same side of the lens
how do magnifying glasses work?
they create a magnified virtual image
the object must be closer to the lens than the focal point
what is the magnification formula to work out the magnification produced by a lens?
magnification = image height/ object height
what is the range of wavelengths for visible light?
violets at 400 nm up to reds at 700 nm
what are the primary colours that are mixed to create every other colour?
pure red, green and blue, they can’t be made by mixing colours. when they are all put together they create white
what do opaque objects do when light hits them?
they absorb some wavelengths and reflect others, they do not transmit any. the colour of the object is determined by which wavelengths are most strongly reflected
what wavelengths do white and black objects reflect?
white objects reflect all of the wavelengths equally
black objects absorb all wavelengths of visible light
how do transparent and translucent objects react to light?
some of the light that hits the surface isn’t reflected or absorbed, its transmitted
how do colour filters work?
they only let some colours through the rest are absorbed. if white light hits a blue filter only blue light is absorbed. colours that are absorbed by the filter are perceived as black when observed through it. e.g. a red hat is black through a blue filter
what does a hot object do in terms of radiation as it cools down?
an object thats hotter than it surroundings emits more IR radiation than it absorbs as it cools down and vice versa
what do objects at a constant temperature do in terms of radiation?
they emit infrared at the same rate that they absorb it
how can different surfaces absorb and emit infrared differently?
black surfaces are better at absorbing and emitting radiation than white surfaces
matt surfaces are better than shiny surfaces
what is a Leslie cube?
a hollow, watertight, metal cube made of aluminium for example. it has 4 faces with different surfaces e.g. matt black, matt white, shiny metal and dull metal
how can an investigation for infrared emission by different surfaces be tested?
fill a Leslie cube with boiling water on a heat proof mat and wait for it to heat up
hold a thermometer to each side, all should be the same temperature
record the amount of infrared radiation each side emits with an infrared detector.
you should find its higher for dark, matt sides
the experiment can be done more than once to show its repeatable
what risk assessment can be done for the Leslie cube experiment?
don’t touch the boiling hot cube or spill boiling water from the kettle
what is a perfect black body?
an object that absorbs all of the radiation that hits it. no radiation is reflected or transmitted.
it is the best possible emitter of radiation
what do the intensity and distribution of the wavelengths an object emits depend on?
they depend on the objects temperature.
as temperature increases so does the intensity of every emitted wavelength.
intensity increases faster for shorter wavelengths this causes peak wavelength to decrease
what is the intensity of a wavelength?
the power per unit area, how much energy is transferred to a given area in a certain amount of time
what determines the earths temperature?
the amount of radiation it reflects, absorbs and emits.
during the day radiation is transmitted from the sun and absorbed so the temperature increases
at night less radiation is absorbed than emitted so temperature decreases
how can changes to the atmosphere affect earths temperature?
if the atmosphere starts to absorb more radiation without emitting the same amount, the overall temperature will rise until absorption and emission are equal again
what are sound waves caused by?
vibrating objects, these vibrations are passed through the surrounding medium as a series of compressions ad rarefactions
what medium to sound waves move faster in?
they move faster in solids than liquids and in liquids faster than gases. it can’t travel through a vacuum e.g. space
how do sound waves cause you to hear?
they make your ear drum vibrate, vibrations pass on to tiny bones in your ear called ossicles, through the semicircular canals and to the cochlea.
the cochlea turn vibrations into electrical signals which are sent to your brain and allow you to sense the sound
what frequencies can humans hear?
20 Hz - 20 kHz
it is limited by the size and shape of your ear drum as well as the structure of the parts of your ear that vibrate to transfer energy from the sound wave
what are echoes?
sound waves can be reflected by hard flat surfaces, echoes are reflected sound waves
what happens when a sound wave refracts as they enter different media?
as they enter denser material they speed up because its wavelength changes but the frequency doesn’t so its speed must also change
what is ultrasound?
mechanical vibrations that produce sound waves beyond the range of human hearing e.g. above 20 000 Hz
what is partial reflection?
when a wave passes from 1 medium into another and some of the wave is reflected off the boundary and some is transmitted
how does ultrasound use partial reflection?
when it passes through an object, some will get reflected at every boundary. the time taken for the reflection to reach a detector is used to measure how far away something is
what different ways can ultrasound be used?
medical imaging
industrial imaging
echo sounding
how can ultrasound be used for medical imaging?
when ultrasound reaches a boundary between 2 different media some of the wave is reflected
the timing and distribution of these echoes are processed by a computer to produce a video image
this can be used for pre-natal scans
it is safer than x-ray
how can ultrasound be used for industrial imaging?
it can be used to find flaws in objects like pipes or materials like wood or metal
ultrasound is reflected by the far side of a material
if there is a crack the wave will reflect sooner
how can ultrasound be used for echo sounding?
it uses high frequency sound waves and is used by boats and submarines to find out the depth of water or locate objects in deep water
what could happen when a wave arrives at a boundary between materials?
it can be completely or partially reflected, it could keep travelling in the same direction at a different speed, it could be refracted or absorbed
what can studying the properties of waves through structures tell us?
it can give us an idea to some of the properties of the structure that you can’t see
what happens when there is an earthquake?
seismic waves are produced which travel through the earth and can be detected all over the surface of the planet using seismometers
what do seismologists do?
they work out the time it takes for the shock waves of an earthquake to reach each seismometer, and which parts of the earth don’t receive shock waves
what happens when seismic waves reach a boundary between different layers of material inside the earth?
some waves will be absorbed and some will be refracted. most of the time if waves are refracted the speed changes gradually so its path is curved. but if the properties change suddenly, the wave changes abruptly and the path has a kink
what are the 2 types of seismic wave?
P-waves and S-waves
how have scientists worked out the internal structure of the earth and the size of the earths core?
by observing how seismic waves are absorbed and refracted scientist have worked out where the properties of the earth have dramatically changed
what are P-waves?
they’re longitudinal,
they travel through solids and liquids
they travel faster than S waves
what are S-waves?
they are transverse
they can’t travel through liquids (or gases) they’re slower than P waves
