p6 waves Flashcards
what do waves transfer?
waves transfer energy in the direction that they are travelling in
what is a medium?
a medium is a substance at which a wave a propagate
what happens when a wave travels through a medium?
the particles of the medium oscillate and transfer energy between eachother. but overall, 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 a wave from it’s undisturbed position
what is the wavelength of a wave?
the distance between the same point on two adjacent waves
what is the frequency of a wave? and what is it measured in?
the number of complete waves passing a certain point per second, it is measured in hertz. one Hz is 1 wave per second
what is the period of a wave?
the amount of time it takes for a full cycle of the wave to pass a point
what is the distinguishing property of traverse waves?
their oscillations are perpendicular to the direction of the energy transfer. for example, a spring wiggling from side-to-side
what are some examples of traverse waves?
1) electromagnetic waves, eg light
2) ripples and waves in water
3) a wave on a string
what is the distinguishing property of longitudinal waves?
the oscillations are parallel to the direction of energy transfer. for example, pushing the end of a spring gets you a longitudinal wave
what are some examples of longitudinal waves?
1) sound waves in the air, eg ultrasound
2) shock waves, eg some seismic waves
what types of waves are all EM waves?
they are all traverse waves, which transfer energy from a source to an absorber. for example, a hot object transfers energy by emitting infrared radiation, which is absorbed by the air
do all EM waves travel at the same speed through air or a vacuum?
yes
what do EM waves form and how are they grouped?
1) they form a continuous spectrum over a range of frequencies.
2) they’re grouped into 7 basic types based on their wavelength and frequency
what are the 7 parts of the electromagnetic spectrum?
LISTED FROM INCREASING FREQUENCY AND DECREASING WAVELENGTH:
1) radio waves
2) microwaves
3) infrared
4) visible light
5) ultraviolet
6) x-rays
7) gamma rays
why is there such a range of frequencies of EM waves?
because EM waves are generated by a variety of changes in atoms and their nuclei - this also can explain why they can absorb different frequencies, cause each one causes a different change
what are EM waves made up of?
oscillating electric and magnetic fields
what are radio waves made by?
oscillating charges
how can you create radio waves?
1) the frequency of the EM waves produced by oscillating current will be equal to the freq of the alternating current.
2) to produce radio waves, you can use the alternating current in an electrical circuit.
3) the object in which electrons oscillate to create radio waves called a transmitter.
4) when transmitted, radio waves reach a receiver, where they are absorbed.
5) the energy transferred by the waves is transferred to the electrons in the material of the receiver. where they then cause the electrons to oscillate, and if the receiver is part of a complete circuit, it generates an AC.
6) this current has the same freq as the radio waves that generated it.
what are radio waves used for?
mainly for communications
how are long-radio waves good for their use?
they can be transmitted and received from halfway around the world.
- this is because they diffract around the surface of the curved earth.
- they can also diffract around hills and into tunnels ect
therefore this makes it possible for radio waves to be received, even if it isnt in the line of the transmitter
how are short-radio waves good for their use?
they can be received at long distances from the transmitter.
- this is because they are reflected from the ionosphere- an electrically charged layer on the Earth’s upper atmosphere
what uses short- radio waves?
bluetooth uses short-radio waves to send data over short distances between devices without wires
why are medium waves good for their use?
can reflect from the ionosphere, depending on the atmospheric conditions and the time of day
what are micro waves used for?
satellites and microwaves
how and why can micro waves be used for satellite communication?
1) the signal from a transmitter is sent from Earth to space.
2) it is picked up by the satelite receiver dish, orbiting thousands of km above earth.
3) the satellite then transmits the signal back to Earth in a different direction.
4) where it is received by a satellite dish on the ground. there is a slight delay due to the long distance.
-MICRO WAVES CAN PASS THROUGH THE EARTHS WATERY CONDITIONS-
how can micro waves be used for microwaves?
1) in the microwave, the micro waves are absorbed by the water molecules in food.
2) the micro waves penetrate the food for up to a few cm before being absorbed and transferring their energy to the water molecules in the food, causing it to heat up.
3) the water molecules then transfer this energy to the rest of the molecules in the food by heating.
what can infrared radiation be used for?
it can be used to monitor and increase temperatures
how can infrared cameras monitor temperature?
1) the camera detects infrared radiation and turns it into an electric signal, which is displayed on the screen as a picture.
2) the hotter the picture is, the brighter it appears
what is the relationship between temperature and infrared radiation?
the hotter an object is, the more infrared radiation is given out
how can infrared radiation increase temperatures?
1) absorbing infrared radiation causes objects to get hotter.
2) therefore, the temperature of food increases when absorbing it. eg a toaster
3) heaters contain a long piece of wire that heats up when a current flows through it. this wire emits a lot of infrared radiation (and a little visible light as it glows).
4) the emitted radiation is absorbed by the air and objects in the room.
5) energy is transferred by the IR waves to the thermal energy stores. causing their temps to increase.
what can visible light be used for?
they can be used optic fibre communications
what are optic cables?
thin glass or plastic fibres that carry data over long distances as pulses of visible light
how to optic cables transmit data?
the reflection of the light waves.
the light waves are bounced back and forth until they reach the end of the fibre.
why can light rays be used for optic fibres?
because light is not easily absorbed or scattered as it travels along a fibre
what can ultraviolet waves be used for?
energy efficient lamps and suntans
what is fluorescence and how is it created?
fluorescence is a property of certain chemicals, where UV radiation is absorbed and then visible light is emitted. thats why fluorescent colours are so bright- they emit light
how are energy- efficient and long- lasting light bulbs?
the fluorescent lights generate UV radiation, which is absorbed and re-emitted as visible light by a layer of a compound called phosphor, in the inside of the bulb.
what is another use of ultraviolet radiation?
it can be used in security pens to mark property with ur name. the ink will only show under a UV light. this can help police identify your property if its stolen
what is ultraviolet radiation produced from?
the sun, this is what gives people a suntan when they’re exposed to it
what is an alternative to sunbathing in the sun?
tanning salons, where UV lamps are used to give an artificial suntan.
however, over exposure to UV radiation can be dangerous (fluorescent light emit very little UV so they’re safe)
what are the uses of gamma and x-ray radiation?
- medical screenings (x-ray)
- radiotherapy (x-ray & gamma)
- medical tracers (gamma rays)
- cleaning medical equipment (gamma)
why can x-rays be used for medical screenings?
x- rays can pass easily through flesh but not so easily through denser materials such as bones or metal.
so its the amount of radiation that is (or is not) absorbed that gives you an x-ray vision.
why can x-rays and gamma rays be used for radiotherapy?
high doses of these rays kill all living cells- so they are carefully directed towards the cancer cells to avoid killing too many normal, healthy cells
what is a medical tracer?
this is where a gamma- emitting source is injected into the patient, and its progress is followed around the body
why can gamma radiation be used as a medical tracer?
because it can pass out through the body to be detected
which EM waves are low energy?
radiowaves
microwaves
infrared waves
visible light
which EM waves are high energy?
ultraviolet
x-rays
gamma rays
what is the effect of radiation dependent on?
how much energy the wave transfers
how much energy do low frequency waves transfer and do they get absorbed?
low frequency waves dont transfer much energy and so they past through soft tissue without being absorbed. this means that they dont cause much damage
how much energy do high frequency waves transfer and how much damage do they cause?
they transfer a lot of energy, therefore they can be very dangerous if exposed to them frequently
how can UV rays cause damage to cells and humans?
they damage surface cells, which can lead to sunburn and cause skin to age prematurely.
some more serious effects are blindness and increased risk of skin cancer
how can gamma and x-rays cause damage to cells and humans?
they are types of ionising radiation. (they carry enough energy to knock off electrons), this can cause gene mutation or cell destruction, or cancer
how do radiographers protect themselves from x-rays and gamma rays?
wear lead aprons and stand behind a lead screen or they leave the room
what is radiation dose?
a measure of the risk of harm from the body being exposed to radiation. this is not a measurement of the total amount of radiation absorbed, as not all radiation that is absorbed is harmful.
- the risk depends on the total amount of radiation and how harmful that type of radiation is
how do radiation risks differ?
because a risk can be different for different parts of the body. for example, if a patient has a CT scan on their chest, they are 4 times more likely to suffer damage to their genes compared to a head scan
how can you measure the speed of sound?
1) attach a signal generator to a speaker to generate sounds with specific frequencies.
2) set up the oscilloscope so the detected waves at each microphone are shown as separate waves.
3) start with both microphones next to the speaker, then slowly move one away until the 2 waves are aligned on the display, but have moved exactly one wave length apart.
4) measure the distance between the microphones to find one wavelength.
5) you can use the given formula to find the speed of the waves passing through the air. the freq is whatever you set the signal generator to.
what are the three things that can happen when a wave arrives at a boundary between two different materials?
1) the wave is absorbed by the material the wave is trying to cross into- this transfers energy to the material’s energy stores.
2) the waves are transmitted- the waves carry on travelling through the new material. this often leads to refraction.
3) the waves are reflected.
what is the rule for all reflected waves?
angle of incidence= angle of reflection
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’ (in terms of reflections) .
an imaginary line thats perpendicular to the surface at the point of incidence. it is usually displayed as a dotted line
when does specular reflection happen?
when a wave is reflected in a single direction by a smooth surface
what is a diffuse reflection?
is when a wave is reflected by a rough surface, and the reflected rays are scattered in lots of different directions
why does a diffuse wave happen?
1) the normal is different for each incoming wave, this means that the angle of incidence is different for each ray. but the rule ‘angle of incidence= angle of reflection’ still applies.
2) when light is reflected by a rough surface, the surface appears matte, and you dont get a clear reflection
what is refraction?
when a wave crosses a boundary at an angle and changes direction
what does the amount of refraction depend on?
how much the wave slows up or speeds down.
- this usually depends on the density of the two materials. the higher the density, the slower it travels as it is more difficult for the waves to pass through the highly compact particles
how can you tell that a wave has slowed down when passing a boundary?
when it bends towards the normal
how can you tell that a wave has sped up when passing a boundary?
when it bends away from the normal
what in a wave stays the same and what changes when refracted?
the wave length changes but the frequency stays the same
when will a wave NOT be refracted when hitting a surface?
when it travels along the normal, however it will change speed
what is the optical density of a material?
a measure of how quickly light can travel through it- the higher the optical density, the slower the light waves travel through it
how can you construct a ray diagram to show refraction?
1) draw the boundary between ur 2 materials and find the normal.
2) draw the incidence ray that meets the normal at the boundary. (use a protractor).
3) draw the refracted ray on the other side of the boundary .
- if the 2nd material is optically denser than the 1st, the angle of refraction is smaller than the angle of incidence.
- if the 2nd material is less optically dense than the 1st, the angle of refraction is larger than the angle of incidence
what are sound waves caused by?
vibrating objects that are passed through the surrounding medium as a series of compressions and and rarefactions
why does sound generally travel faster in solids than in liquids?
because solids have more compacted, therefore the distance between each particle is not far, however this is not the case for liquids and gasses. it is harder for the particles in liquids and gasses to vibrate as they are further away from one another, it takes more time for them to collide
why can sound not travel in space?
because it’s mostly a vacuum, so there are no particles to move or vibrate
how can we hear sounds?
1) sound waves that reach our eardrums can cause it to vibrate.
2) these vibrations pass onto tiny bones in our ear called ossicles, through the semicircular canals and to the cochlea.
3) the cochlea turns these vibrations into electrical signals which get sent to our brain to allow you to sense the sound
what can different materials do to frequencies?
they can convert different frequencies of sound into vibrations. eg: humans can hear sound in range of 20Hz- 20kHz. microphones can pick up on sounds outside of this range, but if you tried to listen to this sound, you wouldnt be able to hear anything
what is human hearing limited by?
the shape and size of our eardrum, as well as the structure of all the parts within the ear that vibrate to transfer energy from the sound wave
what can reflect a sound wave?
sound waves are reflected by hard surfaces. echoes are just reflected sound waves.
how are sound waves refracted?
sound waves are refracted when they enter a different media. as they enter denser material, they speed up.
this is because when a wave travels into a different medium, its wavelength changes but the frequency remains the same, so its speed must also change
how can be used to detect and explore?
1) waves have different properties depending on the material they’re travelling through.
2) when a wave arrives at a boundary between materials it can be completely reflected or partially refracted. the wave may continue travelling in the same direction but different speed, or it may be refracted, or absorbed.
what can happen when a wave arrives at a boundary
when a wave arrives at a boundary between materials it can be completely reflected or partially refracted.
the wave may continue travelling in the same direction but different speed,
or it may be refracted,
or absorbed.
how can waves be used to detect and explore?
1) waves have different properties depending on the material they’re travelling through.
2) studying the properties and paths of waves through structures can give you clues on some of the properties of the structure that you cant see by eyes. this can be done with ultrasounds and seismic waves
what type of wave is produced when an earthquake happens and how can we detect them?
seismic waves are produced which travel through the earth. we can detect then with seismometers.
- seismologists work out the time it takes for the shock waves to reach each seismometer. they also note which areas of earth arent affected
what happens when seismic waves reach a boundary between different layers of material with different properties inside the earth?
some waves will be absorbed and some will be refracted.
- most of the time, if the waves are refracted, they change speed gradually, resulting in a curved path.
- however when the properties change suddenly, the wave speed changes abruptly, and the path has a kink
what have scientists been able to work out due to the observation of how seismic waves are absorbed and refracted?
- where the properties of the earth change dramatically
- one current understanding of the internal of the earth and the size of the earth’s core is based on these observations
what are P-waves?
- they are longitudinal
- they travel through solids and liquids
- they are refracted as the density of the earth changes
- they are faster than S-waves
- they are detected at the bottom of the earth
what are S-waves?
- they are transverse
- they cant travel through liquids or gases
- they are slower than P-waves
- they do not reach the bottom of the earth
what is an ultrasound?
when electrical oscillations of any frequency are converted into mechanical vibrations to produce sound waves beyond human hearing
what happens to ultrasound waves at a boundary?
they get partially reflected
how do ultrasounds work in medical use?
1) the US waves can pass through the body but when they reach the skin of the foetus, some of the waves are reflected back.
2) the exact timing and distribution of the echoes are processed by a computer to produce a video image of the foetus
how can ultrasounds be used to detect flaws in materials such as wood or metal?
1) the US waves are usually reflected from the far side of the material.
2) if there is a crack inside the object, it will be reflected sooner
how do lenses form images?
and what are the two types of lenses, their shape and what they do to light rays?
1) lenses form images by refracting light
CONVEX- bulges outward, and converges parallel light rays.
CONCAVE- caves inward, and diverges parallel light rays.
where is the principal focus of a convex lense?
where the parallel rays that hit the axis all meet after refraction
where is the principal focus of a concave lense?
where the parallel rays hitting the axis appear to all be coming from. you can trace the refracted waves back until they all meet
what is the focal point?
the distance from the centre of the lens to principal focus
what is a real image?
where light from an object comes together to form an image onn a ‘‘screen’
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
what must you mention to describe an image properly?
1) how big it is compared to the object.
2) whether its upright or inverted (upside down).
3) whether it is real or virtual.
how to draw a ray diagram for an image through a convex lens?
1) pick a point on the top of the object. draw a ray going from the object to the lens.
2) draw another line from the top of the object going straight down the middle of the lens.
3) draw a refracted ray from the incident ray that is parallel to the axis through the principal focus.
4) mark where the rays meet and that is the top of the image.
5) repeat same things from the bottom of the object
how does distance from the lens affect the image?
1) an object at 2F will produce a real, inverted image the same size as the object, and at 2F
2) between F and 2F, it’ll make a real, inverted image bigger than the object, and beyond 2F.
3) nearer than F will make a virtual image that is bigger, upright, and at the same side of the lens
how can you draw a ray diagram through a concave lens?
1) pick a point on the top of the object and draw a ray from the object to the lens parallel to the axis.
2) draw a ray from the top of the object through the middle of the axis.
3) the incident ray parallel to the axis is refracted so it seems like it came from the principal focus, so draw a dotted ray from the principal focus (dotted until it reaches the lens)
4) mark where the refracted rays meet, thats the top of your image.
5) repeat for the bottom of the object
what type of image does a convex lens produce?
what type of image does a concave lens produce?
1) both real and virtual
2) only virtual
how do magnifying glasses work?
- they work by using a convex lens to create a magnified virtual image.
1) the object being magnified must be closer to the lens than the focal point.
2) the light rays dont actually come from the place it appears to be because you cant project a virtual image onto a screen.
what is visible light made up of?
a range of colours which have their own narrow range of wavelengths and frequencies
what are opaque objects?
what does the colour of an opaque object depend on?
1) objects that do not transmit light. for example, when VL waves hit them, they absorb some wavelengths of light and reflect others.
2) the colour of an opaque object depends on which wavelengths of lights are most strongly reflected
how is the colour for opaque NON-primary coloured objects made?
- either by reflecting either the wave lengths of the corresponding colour
- or because its reflecting the waves of the primary colours that can mix together to make that colour
what do white objects do with light waves?
what do black objects do with light waves?
what do transparent and translucent objects do?
1) reflect all of the wavelengths of visible light equally.
2) absorb all the wave lengths of visible light
3) either reflect or absorb waves of visible light
what are colour filters and how do they work?
colour filters are used to filter out different wave lengths of light, so that only certain colours are transmitted- the rest are absorbed
what happens with a primary colour filter?
it will only transmit THAT colour.
- however for example, if you look at a blue object through a blue colour filter , it would still look blue as the blue light is reflected from the object and is transmitted by the filter.
- however if the object was a colour that is not made from blue, then the object would appear black because all of the light rays are absorbed by the filter
what happens with non-primary coloured filters?
they let through both wavelengths of light for that colour and the wavelengths of the primary colours that can be added together to make that colour
what is black body radiation?
an object that absorbs all of the radiation that hits it. no radiation is reflected or transmitted
why do all objects emit EM radiation?
because of the energy in their thermal energy stores . this radiation isnt just the infrared part of the spectrum, it covers a range of wavelengths and frequencies
what are good absorbers also?
good emitters
what is the best possible emitter?
perfect black bodies
what is the intensity and distribution of the wavelengths emitted from an object dependent on?
the objects temperature
what is the relationship between the temperature of the object and the intensity of the wavelength?
as the temperature of the object increases, the intensity of each wavelength increases
what is the relationship between the length and intensity?
the shorter the wavelength, the more rapidly intensity increases . this causes the peak wavelength to decrease
what does the overall temperature of the earth dependent on?
the amount of IR radiation it reflects, absorbs and emits
what is the absorption and temperature of the earth like during the day?
- a lot of radiation is transferred to the earth from the sun and it is absorbed.
-this causes an increase in local temperature
what happens to the absorption and temperature of the earth like during the night?
-less radiation is being absorbed than is being emitted.
-therefore the local temperature decreases
how is some radiation reflected or absorbed? (earth and radiation)
by the atmosphere, clouds and the earths surface
how is some radiation emitted? (earth and radiation)
- by the atmosphere
- some radiation emitted by the earths surface is reflected or absorbed (and later emitted) by the clouds
