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