Science- Physics - Waves - P6 Flashcards
what is a wave ?
an oscillation that transfers energy without transferring any matter, making the particles of the substance that it is travelling through oscillate
what is an oscillation ?
a vibration
what are the 2 types of waves ?
transverse
longitudinal
what are transverse waves ?
where the oscillations are perpendicular ( at 90 degrees) to the direction of energy transfer of the wave
where do waves transfer energy ?
in the same direction they travel
give an example of a transverse wave ?
light
other electromagnetic waves
what are longitudinal waves ?
waves with oscillations along the same line they travel with areas of compression and rarefaction, the oscillations are parallel to the direction of energy transfer of the wave
what is rarefaction ?
where the particles are spread out
what is compression ?
where the particles are bunched together
give an example of longitudinal waves ?
sound waves
a spring when you push the end
do waves transfer matter ?
no
what happens in waves ?
they travel through a medium and the particles of the medium oscillate and transfer energy between each other but overall the particles stay in the same place, only energy is transferred
what are crests and troughs ?
points of maximum positive and maximum negative displacement from the particles rest position
what is the amplitude ?
the maximum displacement of a point on the wave from its undisturbed position - the distance from the undisturbed position to a crest or trough
what is a wavelength ?
the distance between the same point on 2 adjacent waves
what is the frequency ?
the number of complete waves passing a certain point per second
what is frequency measured in ?
hertz
what is the period of a wave ?
the amount of time it takes for a full cycle of the wave to be completed - the length of time between 1 crest passing a point and the next crest passing the same point
what is wave speed ?
the speed at which energy is being transferred
how do you measure the speed of sound in air ?
find the frequency and the wavelength of a sound wave
how can you generate a sound wave ?
- using a specific frequency
- attach a signal generator to a speaker
- the sound wave can then be detected by microphones
- these convert it to a trace on an oscilloscope
describe the method of how to measure the speed of sound in air ?
- set equipment up with both microphones next to the speaker, the detected wave at each microphone can be seen as a separate wave on the oscilloscope
- slowly move the microphone away from the speaker, its wave will shift sideways on the oscilloscope keep moving until the 2 waves on the oscilloscope are aligned again, at this point the microphones will be exactly 1 wavelength apart so measure the distance between them
why are water ripples useful for investigating wave properties ?
they are visible
what do you use to produce waves ?
a signal generator
what equipment do you need when measuring the speed of water ripples ?
a ripple tank which is made of glass
why do you use a ripple tank ?
to show the properties of waves as the glass bottom of the tank means light can be shone onto the tank from above to project the wave pattern onto a screen below
how do you carry out the measuring the speed of water ripples experiment ?
- set up equipment
- fill ripple tank with water of a depth of 5mm
connect dipper to a signal generator and set it off at a known frequency - dim lights and turn on lamp to see wave pattern
- the distance between each shadow line = 1 wavelength
- measure the distance of 10 ripple waves and divide by 10 to get wavelength using a ruler
what do you need to observe waves on a string ?
- taut string
- vibration transducer
what is a vibration transducer ?
something that will convert an electrical signal from a signal generator into vibrations
how can you ensure the string is taut ?
by connecting one end of it to a vibration transducer and passing it over a pulley with masses hanging from the other end
how do you carry out the observing a wave on a string practical ?
set up equipment and turn on signal generator and vibration transducer
- string will start to vibrate
- adjust frequency of signal generator until there’s a clear eave on the string
- measure the wavelength of the waves created
best way to do this is measure the length of 4/5 waves and divide by 4/5 to get the average half- wavelength then double
-
what 3 things can happen when waves arrive at a boundary between 2 different materials ?
- absorption
- reflection
- transmission
what is absorption ?
- waves may be absorbed by the material
- the wave is trying to cross into this transfers energy into the materials energy stores
what is reflection ?
the waves may bounce back
what is transmission ?
waves may be transmitted which means they carry on travelling through the material however they often undergo refraction
what is refraction ?
when the wave reaches a boundary at an angle and changes direction
what is a ray ?
a straight line showing the path a wave travels along
how do you draw a ray diagram ?
- draw the boundary between the 2 materials and then add inthe normal
- draw an incoming incident ray that meets the normal at the boundary, the angle which is between the ray and the normal is the angle of incidence
- draw the refracted ray on the other side of the boundary the angle that the refracted makes with the normal is called the angle of refraction
- the angle of refraction could be smaller than the angle of incidence or bigger
what is the angle of incidence ?
the angle between the ray and the normal
what is the angle of refraction ?
the angle that the refracted ray makes with the normal
when is the angle of incidence greater than the angle of refraction ?
when light moves from air into a glass block
when is the angle of incidence smaller than the angle of refraction ?
when light moves from glass into the air
if the ray passes along the normal and hits the boundary at 90 degrees what happen ?
it will pass through without changing direction, the angles of incidence and refraction will be at 0 degrees
why does refraction occur ?
waves travel faster in some materials than others so the speed of a wave can change as it crosses a boundary
when a wave refracts what happens to it speed and frequency and wavelength ?
its speed changes but its frequency stays the same
wavelength increases/decreases with speed
what is the optical density of a material ?
how quickly light travels through it, the higher the optic density, the slower the light travels
what are wavefronts ?
imaginary lines drawn through certain points on waves, e.g through each crest and are perpendicular to the direction where the wave is moving
when are wavefronts closer together ?
in more optically dense materials, showing the decrease in wavelength
why are wavefront diagrams useful ?
to explain why refraction happens
how do waves refract ?
- when a wave crosses a boundary into a new substance at an angle to the normal one end of it enters the new material before the rest of the wave
- this means that end of the wave enters the enw material before the rest of the wave and changes speed before the rest of the wave causing the wave to change direction and refract
what does which way the wave bends depend on ?
- whether it moves faster or slower in the new medium
if the wave slows down at a boundary, what happens ?
it bends towards the normal
if a wave speeds up at a boundary what happens ?
it bends away from the normal
as well as being refracted, what could also happen to a wave between 2 materials ?
it could be reflected
how do you show reflection in a ray diagram ?
draw the incoming ray and the reflect ray as well as the normal
what is the law of reflection ?
angle f incidence = angle of reflection
what is the angle of reflection ?
the angle between the reflected wave and the normal
what is specular reflection ?
when parallel waves are reflected in a single direction by a smooth surface
give an example of specular reflection ?
when light is reflected by a mirror
what is diffuse reflection ?
when parallel waves are reflected by a rough surface and the reflected waves are scattered in lots of directions
in diffuse reflection, what is the angle of incidence and why ?
equal for the angle of reflection for each ray, however the tiny bumps on the surface mean the normal ray is different so the angle of incidence is different for each ray
when light is reflected by a rough surface what happens ?
the surface appears matt and unclear
what conditions are experiments of light best in ?
a dim room
why are ray boxes or lasers used ?
to produce thin rays of light so you can see the middle of the ray when tracing it and measuring angles from it
how do you carry out the investigating refraction practical ?
- place a transparent rectangular block on a piece of paper and trace around it
- use a ray box to shine a ray of light at the middle of 1 side of the block
- trace the incident ray on the paper and do the same for the light ray that emerges on the other side of the block
- remove the block and with straight lines join up the lines of the incident and emerging ray this shows the path of the refracted ray
- draw the normal point where the 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 using blocks from different materials keeping the incidence angle the same throughout
why do we carry out the investigating refraction practical
to see how the boundaries of different substances refract light by different amounts
why do we carry out the investigating reflection practical ?
to see how surfaces reflect light in different ways depending on how smooth they are
how do you carry out the investigating reflection practical ?
- take a piece of paper and draw a straight line across it
- place straight edged object on the paper so it lines up with this line
- shine a ray of light at the objects surface and trace the incoming and reflected light beams
- add in a normal line which meets the surface at the point of incidence
- draw and label the incident and reflected rays
- use a protractor to measure the angle of incidence and the angle of reflection and record these values in a table
- also measure the length of the reflected ray and how bright it is
- repeat with a range of objects
what should the results of the investigating reflection practical be ?
smooth surface like mirrors give clear reflections whereas rough surfaces cause diffuse reflection where the reflected beams are wider and dimmer
how do lenses form images ?
lenses form images by refracting light and changing its direction
what are the 2 type of lenses ?
convex (converging)
concave ( diverging)
what is a convex lens ?
a lens which bulges outwards, it causes rays of light which are parallel to the axis of the lens to converge (come together) at the principle focus
what is the axis of the lens ?
a line passing through the middle of the lens, perpendicular to the lens
where is the principle focus of a convex lens ?
where rays hitting the lens parallel to the axis all meet
what is the focal length ?
the distance from the center of the lens to the principle focus
where is there a principle focus ?
on each side of the lens
where will rays from convex lenses parallel to the axis focus ?
on the principle focus on the far side of the lens in relation to where the rays are coming from
what are the 3 main rules for convex lenses ?
- an incident ray travelling parallel to the axis refracts through the lens and passes through the principle focus on the other side
- an incident ray passing through the centre of the lens carries on in the same direction
- an incident ray passing through the principal focus before meeting the lens refracts through the lens and travels parallel to the axis
what is a concave lens ?
a lens which caves inwards , it causes parallel rays to diverge (spread out)
what is the principle focus of a concave lens ?
it is the point where rays hitting the lens parallel to the axis appear to all come from
what are the 3 rules for concave lenses ?
- an incident ray travelling parallel to the axis refracts through the lens and travels in line with the near side principle focus
- an incident ray passing through the centre of the lens carries on in the same direction
- an incident ray passing through the lens towards the far side principal focus refracts through the lens and travels parallel to the axis
what are the 2 types of images ?
real
virtual
what is the type of image produced dependent on ?
whether the 2 light rays coming from the same point on an object will eventually meet
how is a real image formed ?
when the light rays from a point on an object come together to form an image
the light rays actually pass through the same point
what can a real image be captured on ?
a screen - like the image formed on an eyes retina
how is a virtual image formed ?
when the light rays from a point on an object are diverging after they have left the lens so the light from the point on the object appears to be coming from a completely different place
in virtual images do light rays pass through the point >
?
no, they just appear to
give an example of a virtual image ?
a mirror
where can you get a virtual image ?
when looking at an object through a magnifying lens as the virtual image looks bigger than the object actually is
what do you need to say when describing an image ?
how big it is compared to the object
whether its upright or inverted, relative to the object
whether its real or virtual
what is a ray diagram ?
a diagram showing the paths taken by light rays through a lens
what do ray diagrams help with ?
work out what an image formed by the lens will be like
how do you draw a ray diagram for convex lenses ?
- draw a ray form the top of the object that passes straight through the centre of the len without changing direction at all
- draw a second ray from the top of the object that travels parallel to the axis, the ray should refract at the lens so it passes through the principal focus of the lens, the rays may or may not meet
- repeat to check
- draw the image, the point where the 2 rays from the top of the object meet is where the top of the image is formed. The point where 2 rays from the bottom of the object meet is where the bottom of the image is formed
when the bottom of the object is on the axis, what is also on the axis ?
the bottom of the image
what does the type of image formed by a convex lens depend on ?
where the object is placed in relation to the principal focus
what will an object beyond 2F produce ?
a real, inverted image that is smaller than the object, it will sit between F and 2F on the far side of the lens
what will an object placed at 2F produce ?
a real, inverted image that is the same size of the object, it will sit at 2F on the far side of the lens
what will an object placed between F and 2F produce ?
a real, inverted image that is bigger than the object, it will sit beyond 2F on the far side of the lens
what will an object placed between the lens and F produce ?
a virtual image that is the right way up but bigger than the object and the same side of the lens as the object
how do you draw ray diagrams for concave lenses ?
- draw a ray from the top of the object that passes straight through the centre of the lens without changing direction at all
- draw a 2nd ray from the top of the object that travels parallel to the axis, the ray should refract at the lens so that it appears to have to come from the near side principal focus , draw a virtual ray from that principal focus to where that ray meets the lens
- repeat the process
- draw the image , where the real and virtual rays from the top of the object meet is where the top of the image is formed, where the real and virtual rays from the bottom of the object meet is where the bottom of the image is formed
what does a concave lens always produce ?
a virtual image, the right way up, smaller than the object and on the same side of the lens as the object
convex lenses converge light wheras concave lenses …
diverge light
where do rays parallel to the axis converge onto on a convex lens ?
principal focus, but diverge so that they appear to have come from the principal focus of a concave lens
what can convex lenses produce ?
real and virtual images
what can concave lenses produce ?
virtual images
what type of lenses do magnifying glasses use ?
convex lenses
how do magnifying glasses work ?
by creating a virtual, upright image that is larger than the object and is on the same side of the lens as the object for this to happen the object being magnified must be closer to the lens than the focal length
in magnifying glasses, why don’t the light rays come from the place where the image appears to be ?
as it is a virtual image
why doesn’t magnification have a ratio ?
it is a ratio so as long as the units are the same for both you can measure heights in whatever lengths you like
what are sound waves ?
longitudinal waves of vibrating particles caused by vibrating objects
in sound waves, what are the vibrations passed through the surrounding matter as ?
compressions and rarefactions
what can the surrounding matter in sound waves be \/
solid liquid or gas
what matter does sound generally travel best in ?
solids
why is refraction hard to spot in sound waves ?
they are spread out a lot
what happens when a sound wave enters a denser medium ?
it speeds up
if speed increases in sound waves when entering a denser medium, what happens to the wavelength ?
it increases
how does sound travel through solids ?
when the sound wave meets a solid object:
- air particles hitting the object cause the closest particles in the solid to move back and forth
- these particles hit the next particles along and so on
- this series of vibrations passes a sound wave through the objecy
what depends on whether a sound wave can cause an entire solid object to vibrate ?
the type of solid material
frequency of the sound wave
what causes your ear drum to vibrate ?
sound waves of certain frequencies
what vibrations that have reached your eardrum pass onto ?
*tiny bones in your ear called ossicles through the semicircular canals and to the cochlea, the cochlea turns these vibrations into electrical signals which get sent to your brain and allow you to sense the sound
what can humans only hear sounds with frequencies between ?
20 Hz and 20 KHz
what are the limits of the frequencies humans can hear due to ?
the size and shape of our eardrum
structures of parts within the ear that vibrate and transfer energy form the sound wave
what are ultrasound waves ?
sound waves with frequencies greater than 20KHz
who can ultrasound not be heard by ?
humans
how is ultrasound produced ?
electrical devices can be made which produce electrical oscillations of a large range of frequencies, these can be converted into mechanical vibrations to produce sound waves above 20KHz
what is partial reflection ?
when waves pass from one medium into another some waves are reflected by the boundary between the 2 media and some are transmitted
what does partial reflection mean for ultrasound ?
you can point a pulse of ultrasound at an object and wherever there are boundaries between one substance and another some of the ultrasound gets reflected back
what happens when sound waves are reflected by surfaces?
there is a delay between you hearing the original sound and the reflected sound because the reflected sound waves have to travel further to reach your ears
what are reflected sound waves known as ?
an echo
what can the time it takes for the reflections to reach a detector be used to measure ?
how far away the boundary is
what can happen when a wave arrives at a boundary between materials ?
the wave can be :
- completely reflected
- partially reflected
- continue travelling at the same direction but a different speed
- be refracted
- be reabsorbed
what can studying properties and paths of waves through structures tell you ?
clues to some of the properties of the structure you can’t see by the eye - do this with seismic waves, ultrasound waves
what does ultrasound help with ?
imaging or locating objects we can’t see
give examples of what ultrasound can be used for ?
medical and industrial purposes,
echo sounding which can be used in the military or commercial fishing
what is medical imaging ?
ultrasound is used in medicine to see inside the body which allows doctors to diagnose medical conditions inside your body
what is industrial imaging ?
ultrasound is used in industry to see inside materials and products to check that they are suitable for use
what is echo sounding ?
a type of sonar used by boats and submarines where high frequency sound waves are used to find out the depth of the water they are in or to locate objects deep in water
how does echo sounding work ?
a pulse of sound waves is emitted by the boat or submarine and then the time taken for the echo to return is measured, it can be used to calculate the distance to the object that reflect the sound, if you know the speed of sound in the water
when there’s an earthquake what is produced ?
seismic waves which travel out through earth
what are the 2 types of seismic waves ?
p - waves
s - waves
what are p - waves ?
longitudinal waves which can travel through solids and liquids
what matter do p - waves travel better through ?
solids
which type of seismic wave travels faster ?
p - waves
what type of materials do p and s waves travel faster through ?
denser materials
when there’s an earthquake what are the seismic waves produced at different points on the surface of the planet detected by ?
seisometers
what do seismologists do ?
work out the time it takes for the shock waves to reach each seismometer , and note which parts of the earth don’t receive the shock waves at all
they do this to gather information about the inner structure of the earth
what happens when the medium seismic waves travel through changes suddenly ?
the direction changes abruptly and causes a kink
by measuring seismic waves at various points on earth, what can seismologists build up a picture of ?
the paths the waves have travelled along from the point of the origin to the points of detection and work out where any boundaries between different materials occur within the earth
where can s- waves not pass through ?
the core
what have different observations of the earth led seismologists to develop ?
a model of the internal structure of the earth
what are electromagnetic waves ?
a group of transverse waves
what are electromagnetic waves sometimes referred as ?
electromagnetic radiation
what do electromagnetic waves consist of ?
vibrating electric and magnetic fields which is why they can travel through a vaccum
what don’t electromagnetic waves rely on ?
vibrating matter
what do EM waves form ?
a spectrum of waves with different wavelengths, the spectrum is continuous so there are no gaps in it
what does the EM spectrum being continuous mean ?
there are no gaps in it
what is the EM spectrum ?
a continuous spectrum of all the possible wavelengths of electromagnetic waves
how many groups are EM waves put in ?
7
what depends on the group an EM wave is put in ?
their wavelengths (or frequencies)
What speed do EM waves travel at ?
the same speed - 3x10 to the 8 m/s - THE SAME SPEED
do EM waves travel at the same speed ?
yes - in a vaccum - SO YES
where do EM waves transfer energy ?
from a source to an absorber
how can EM waves be produced ?
by changes inside atoms - either to the arrangement of electrons or within the nucleus
how is an EM wave formed when an electron changes ?
if an atom absorbs energy some of its electrons move to higher energy levels within the atom
when each electron falls back down to its original level an EM wave is produced
the higher the frequency of an EM wave the …
more energy it transfers
why do EM waves have a large range of frequencies ?
lots of possible changes can happen within atoms and molecules
what does the number of possible changes within atoms allow ?
a wide range of frequencies of EM radiation to be absorbed by electrons
where do gamma rays come from ?
changes in the nuclei of atoms
what happens in a nuclear change in atoms ?
- unstable nuclei of radioactive atoms decay give out particles
- after spitting out a particle, the nucleus might need to get rid of extra energy
how does a nucleus get rid of extra energy ?
through gamma rays
how are radio waves produced ?
- using an ac current in an electrical circuit
- as ac current is made up of oscillating charges, when the charge oscillates they produce oscillating electric and magnetic fields = EM waves = radio waves
what will the frequency of a radio wave be equal to ?
the frequency of the ac current
what is the object in which the charge oscillates to create the radio wave called ?
a transmitter
how are radio waves recieved ?
- when transmitted waves reach a reciever the radio waves are absorbed
- the energy carried by the waves is transferred to the kinetic energy stores of the electrons in the material of the reciever
- this causes electrons to oscillate and if the reciever is part of a complete electrical circuit it generates an ac
what are radio waves used for ?
- radio and tv signals
how are radio and tv signals sent out ?
by transmitters and recieved by TV or radio aerials
what are long wave radio waves used for ?
- they are transmitted and recieved halfway round the world
how can longwave radio waves transmitted and recieved halfway round the world ?
long wavelengths diffract (bend) around the curved surface of the earth
why are long wave radio waves used ?
- they make it possible for radio signals to be recieved even if the reciever isn’t in the line of sight of the transmitter
what are short wave radio ?
signals that don’t diffract around the earths curve but can still be recieved at large distances from the transmitter
what are short wave radio signals reflected between ?
earth and the ionosphere
what is the ionosphere ?
an electrically charged layer in the earths upper atmosphere
what uses short wave radio signals ?
bluetooth to send data over short distances between devices without wires
what is medium wave radio ?
signals which can reflect from the ionosphere depending on the atmospheric conditions and the time of day
what do medium wave radio signals depend on ?
- atmospheric conditions
- time of day
how do you get reception from TV signals and FM radio ?
you need to be in direct sight of the transmitter as the signal doesn’t bend around hills or travel far through buildings
what type of wave does communication to and from satellites use ?
microwaves
why do communication to and from satellites use microwaves ?
certain wavelengths of microwave can easily pass through the earths atmosphere without being reflected refracted diffracted or absorbed so they can reach satellites
give examples of what satellite communications is used for ?
satellite TV
satellite phones
internet
military communications
how do satellite communications work ?
the signal from a transmitter is transmitted into space where it is picked up by the satellites reciever orbiting above earth
the satellite transmits the signal back to earth in a different direction, where its recieved by a satellite reciever on the ground
why is there a slight delay between when when the satellite transmits the signal back to earth and when its recieved by a satellite reciever on the ground ?
there is a long distance the signal has to travel
how are microwaves used in cooking ?
microwaves used in microwave ovens have wavelengths which allow them to be absorbed by water molecules in food
how do food microwaves work ?
- the microwaves penetrate up to a few centimeters into the food before being absorbed and transferring the energy they are carrying to the thermal energy stores of the water molecules in the food, causing the water to heat up
water molecules then transfer this energy to the rest of the molecules in the food which cooks it
what are the uses of infrared radiation linked to ?
temperature
how is infrared radiation linked to how hot the object is ?
the hotter the object, the more IR radiation it gives out
what are infrared cameras used for ?
to detect IR radiation
monitor temperature
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
how can food be cooked using IR radiation ?
the temperature of the food increases when it absorbs IR radiation
how do electric heaters use IR radiation ?
they contain a long piece of wire that heats up when current flows through it
this wire then emits lots of IR
IR radiation is absorbed by objects and the air in the room
energy is transferred by IR waves to the thermal energy stores of the objects causing their temperature to increase
what can optical fibres ?
thin glass or plastic fibres that can carry data over long distances
why is visible light used in fibre optic cables ?
when the light hits the walls of the fibres it is reflected back into the the fibre which means light is reflected back and forth until it reaches the end of the fibre
why is visible light useful for fibre optic cables ?
it will travel down the fibre without being absorbed or scattered much so the signal is hardly weakened
what is ultra-violet radiation produced by ?
the sun
what can exposure to UV radiation give us ?
suntan
how is UV radiation used in suntan lamps ?
UV lamps can give people artificial suntan
how is UV radiation used in security ink ?
when UV radiation hits fluorescence it is absorbed and visible light is emitted
why are security pens used ?
to mark valueable items to help identitfy your property if it is stolen
how do energy efficient lamps use UV radiation
fluorescent lamps have glass tubes which are coated on the inside with a fluorescent material and are filled with mercury and noble gases
when the electrical current is switched on electrons in the mercury atoms are excited to higher energy levels
when the levels fall back down energy is released as UV radiation
The UV radiation hits the fluorescent coating and is converted to visible light
what are x rays and gamma rays useful for ?
medicine
how are x rays and gamma rays used for medical imaging ?
- radiographers take x rays of people by x rays passing easily through flesh but not easily through denser materials such as bones
what gives you an x ray image ?
the amount of radiation that is absorbed
what do x rays help you see ?
bones if they are broken
how are x rays directed through a patient ?
by a detector plate
how does a detector plate work ?
it starts off white and the bits exposed to the fewest x rays remain white
the bits where x rays have passed through the soft tissue without being absorbed turn black
where is the part of an x ray where the plate has been exposed to the fewest x rays ?
the areas where x rays have been absorbed by bone
what kind of image is an x ray ?
a negative x ray
how are gamma rays used as medical tracers ?
a gamma eating isotope can be traced as it travels through the body because gamma rays can easily pass through the body to be detected
what is radiotherapy ?
radiographers use x rays to treat people with cancer
how are x rays and gamma rays used in radiotherapy ?
high doses of them kill living cells so they are directed towards cancer cells
why does great care have to be used when doing radiotherapy ?
it can kill too many normal cells
what does the effect of each type of radiation depend on ?
how much energy the wave transfers
how much energy do low frequency waves transfer ?
not a lot of energy
how much energy do high frequency waves transfer ?
lots of energy
give an example of a low frequency wave ?
radio wave
give an example of a high frequency wave ?
gamma rays
x rays
what does UV radiation cause ?
damage to the surface of cells
leads to sunburn - causes skin to age prematurely
they can damage the eyes which can lead to blindness and an increased risk to skin cancer
what type of radiation is x rays and gamma rays ?
ionising radiation
what does x rays and gamma rays having ionsing radiation mean ?
they have enough energy to knock electrons off atoms which can kill cells, or cause gene mutations or cancer
what is radiation dose measured in ?
sieverts
what is radiation dose ?
a measure of the risk of harm from the body being exposed to radiation
what does radiation dose take into account ?
- the total amount of radiation absorbed
- how harmful the type of radiation is
- the type of body tissue absorbing the radiation as some types of body tissue are more easily damaged by radiation than others
what part of the EM spectrum can we see ?
the visible light spectrum
what are the wavelengths of of violet on the EM spectrum ?
380 - 450 nm
what is the wavelength of red in the EM spectrum ?
620-750 nm
what are the primary colours ?
red green blue
what happens when all the colours in the visible light spectrum are put together ?
it creates white light
what are opaque objects ?
objects which do not transmit light
what happens when visible light waves hit opaque objects ?
they absorb some wavelengths of light and reflect others
what does the colour of an object depend on ?
which wavelengths of light are most strongly reflected
why may a banana look yellow ?
it is reflecting yellow light OR it is reflecting both red and green light
why do objects appear white ?
they reflect all of the wavelengths of visible light equally
why do objects appear black ?
they absorb all the wavelengths of visible light
what kind of objects can transmit light ?
transparent
translucent
how do transparent objects transmit light ?
in straight lines so you can see an image clearly through them
how do translucent objects transmit light ?
they also scatter light so you can’t see clearly through them
do transparent and translucent objects transmit all light ?
no, they still may absorb or reflect some
what is a transparent or translucent objects colour related to ?
the wavelengths of light transmitted and reflected by it
what does a colour filter do ?
it only transmits certain wavelengths and absorbs other wavelengths
what effect does a colour filter have ?
they only let some colours through
what happens if you look at a blue coloured object through a blue colour filter ?
it will still look blue because the blue light reflected from the objects surface is transmitted by the filter
if a red object was looked at through a blue filter what happens ?
it appear black because all of the light reflected by the object will be absorbed by the filter
what do all objects continually emitt ?
infrared radiation
the hotter an object is, what effect does this have on the amount of IR radiation it emitts ?
it emitts more
what does the temperature of an object depend on ?
the balance between the amount of IR radiation than it absorbs and the amount of IR radiation it emits
what does an object that is hotter than its surroundings do ?
emit more IR radiation than it absorbs - so its temperature falls
what does an object that is cooler than its surroundings do ?
absorb more IR radiation than it emits so its temperature rises
when an object is at the same temperature as its surroundings, what happens ?
it emits IR radiation at the same rate as it is absorbing it and its temperature will be constant
how do some colours and surfaces emit radiation better than others ?
black absorbs radiation better than a white one
a matt surface absorbs radiation better than a shiny one
what is a leslie cube ?
a hollow, water tight cube which is made of metal - the four vertical faces of the cube have different surfaces
what are leslie cubes useful for ?
investigating IR emission by different surfaces
describe step by step, how to investigate IR emissions using a leslie cube ?
- place an empty leslie cube on a heatproof mat and fill with boiling water
- wait for the cube to warm up then hold a thermometer against each of the 4 vertical faces of the cube
- check all the faces are the same temperature
- hold an IR detector at a set distance away from one of the cubes vertical faces and record the amount of IR radiation it detects
- repeat this measurement for each of the cubes faces
what are the risks when doing a leslie cube experiment ?
- don’t move the cube with boiling water
- take care when carrying the kettle of boiling water when pouring water in the cube
what are the results from the leslie cube experiment ?
IR radiation detects more on darker surfaces and matt surfaces
how can you show how IR radiation absorbed by different material depends on the material ?
- set up 2 ball bearings stuck to one side of a metal plate with solid pieces of candle wax the other sides of these plates are faced towards the flame
- the sides of the plates facing the flame have a different surface colour
- the ball bearing on the plate with the black plate will fall first as the black surface absorbs more IR radiation
what does the overall temperature of the earth depend on ?
the rates at which radiation is reflected, absorbed and emitted
why is it hotter during the day ?
more radiation is absorbed than emitted
why is it cooler in the night ?
less radiation is absorbed than emitted
why does the earths overall temperature remain fairly constant ?
the overall amount of radiation absorbed from space is equal to the amount of radiation reflected into space
what is a perfect black body ?
an object that absorbs all of the electromagnetic radiation that hits it
why are black bodies perfect emitters of radiation ?
a good absorber is a good emitter
what does the amount and type of radiation depend on ?
the objects temperature
what is the intensity ?
power per unit area - how much energy is transferred to a given area in a certain amount of time
as the temperature of an object increases, what happens to its intensity ?
the intensity of every emitted wavelength increases
if the temperature of an object increases what happens to the peak wavelength ?
it decreases
when an object gets hotter, does the intensity increase more rapidly for shorter or longer wavelengths?
shorter
why does intensity increase more rapidly for shorter wavelengths when an objects temperature increases ?
a bigger proportion the radiation is emitted by a hot object has a short wavelength compared to that emitted by a cooler object
