list the electromagnetic spectrum in order
radio waves, microwaves, infrared, UV, x rays, gamma rays
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what speed do all waves in the EM spectrum transmit through a vacuum
300 00km/s
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what does the energy of a wave increase with
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what are photons
packets of energy that EM waves travel in
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how do the energy in the photons increase
an increase in frequency of the wave
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what do solar cells do
produce electricity. they absorb EM radiation from the sun and transfers the energy to electrical energy
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what does the amount of energy absorbed by an EM wave, depend on
number of photons per second, energy transferred by each photon (wave intensity)
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why does the intensity of a wave decrease with distance
the energy is spread out as it gets further away from its source
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what is the intensity of a wave in the vacuum inversely proportional
the square of the distance from its source
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what happens if the wave is partially absorbed by the medium its passing through
the intensity decreases rapidly
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what charge do electrons have
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what charge do ions have
they can be positive or negative
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what charge do atoms and molecules have
no charge overall
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how are atoms and molecules ionised
when they lose electrons
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name the three ionising radiations in the EM spectrum
UV, X ray and Gamma
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what can ionisation of a molecule set off
a chemical reaction
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what do radioactive materials emit
gamma rays
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what can gamma rays do
travel through the human body easily
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how do x rays work
they pass through muscle but are absorbed by bone
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what happens if cells absorb gamma rays
they can be ionised and damaged, the damaged cells can die or develop into cancer
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how are hospital workers protected from ionising radiation
lead and/or concrete screens
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why can X rays be used to show shadow pictures of peoples bones
x rays are absorbed by dense materials
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what happens when things absorb radiation
they heat up
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what happens if cells get too hot
they can be damaged
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why do cells heat up when they absorb radiation
cells contain water molecules. when water molecules are heated they vibrate and that energy is shared with surrounding molecules
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explain how microwave ovens are safe
they have metal doors so the micro waves are absorbed or reflected, they don't escape
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why are people concerned about mobile phones
they use low intensity micro waves, meaning there is a heating effect. people are worried about the health risks of the radiation
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how is cell damage from mobile phones measured
by comparing cancer rates in large groups of people who do and do not use mobile phones
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what radiation does sunlight cause
UV (ultra violet)
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what does ultra violet radiation cause
sunburn and skin cancer
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how do sunscreens and clothing protect people from sunlight
they absorb the UV radiation
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what is the Ozone
a layer at the top of the atmosphere that absorbs UV, this protects living things from any harmful effects of UV
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what percentage will the risk of skin cancer be if the ozone thins by 1%
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describe what UV radiation does to the Ozone layer
causes chemical changes to molecules in the ozone
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what happens to the earth when it absorbs radiation
it warms up
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what is the greenhouse effect
radiation from the earth passing into space, it is reflected off clouds and radiated back to earth from gasses which absorb it. this keeps the earth warm.
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what radiation cools the earth down
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what is the principal frequency
the one with the greatest intensity
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why does radiation from the sun have a higher frequency than radiation from the earth
the sun is hotter, principal frequency increased with temp
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what is one of the main greenhouse gasses found in the earths atmosphere
carbon dioxide
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why have rates of CO2 increased
deforestation and burning fossil fuels
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increase in the earths temp correlates with the rise in CO2 levels, why
scientists believe itis caused by CO2 levels as it is a greenhouse gas
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what is global warming
the greenhouse effect increasing the average worldwide temp
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what can global warming cause
change in what crops grow, flooding due to ice caps melting
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three gasses in the atmosphere responsible for the greenhouse effect
wate vapour, carbon dioxide, methane
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why do models suggest global warming will result in more extreme weather
more water vapour in a hotter atmosphere, increased convection increasing wind
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how can radio and micro waves carry tv and radio broadcasts
they are not absorbed by air
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why can infrared be used for internet and long distance telephone communications
hey are not easily absorbed by the glassof optical fibres
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what do radio waves use to transfer info
a carrier wave
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what is modulation
information from the carrier wave, is used to change the amplitude and frequency of the carrier
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what does a radio receiver do
demodulates the carrier wave to recover the info
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what is an analogue signal
an example is sound. varies with any value.
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what is a digital signal
an example is sound or a picture, only has values of 1 and 0
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what happens when an analogue signal is sent by a radio wave in a digital code
value of the signal is measured. value is coded as 1s and 0s. the 1s and 0s make a digital signal by pulsing the carrier on and off. process repeated many times a second
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another word for a radio receiver recovering a signal
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unwanted information is called noise, what does it do
effects radio waves, changes the amplitude of the carrier, reducing the quality of the signal recovered.
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why is it easier to recover signals in a digital recover
the values are 0 or 1
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what is digital info stored as
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what is a byte
a string of eight binary digits, each binary digit can be 1 or 0
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how does digital information make photos
digital info builds up images from tiny dots called pixels. more binary digits will increase the sharpness and quality of the image
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how does digital information make sound
digital information builds up sound from a series of values called samples, more binary digits will increase the sound quality.
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what is an advantage of using digital signals
easily stored in electronic memories, so can be processed by computers
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Other cards in this set

Card 2


what speed do all waves in the EM spectrum transmit through a vacuum


300 00km/s

Card 3


what does the energy of a wave increase with


Preview of the front of card 3

Card 4


what are photons


Preview of the front of card 4

Card 5


how do the energy in the photons increase


Preview of the front of card 5
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