Physics OCR, P2

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How may radiation from one object affect another?
a source emits radiation, which travels outwards from the source and can be reflected, transmitted or absorbed by materials it encounters. Radiation may affect another object when it is absorbed
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How does a beam of electromagnetic radiation transfer energy?
in 'packets' of energy called photons
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What does a higher frequency of electromagnetic radiation mean?
more energy is being transferred by each photon
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What is the order of the electromagnetic spectrum?
radio waves, micro waves, infrared rays, visible light, ultraviolet rays, x-rays and gamma rays
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What speed does electromagnetic radiation travel through a vacuum?
300,000 km/s
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How is the intensity of a beam measured?
the amount of energy arriving at a square metre of surface each second
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What does the energy transferred to an absorber by a beam of electromagnetic radiation depend on?
the number of photons arriving per second and the energy of each photon
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What happens to the intensity of electromagnetic radiation as it travels further?
the intensity decreases because photons spread out as they travel, some photons are absorbed by particles in substances they pass through and some photons are reflected and scattered by other particles
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What can ultraviolet radiation, x-rays and gamma rays do?
have enough energy to change atoms or molecules, which can initiate chemical reactions. Can cause ionisation
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What is ionisation?
when electromagnetic radiations have high enough photon energy to remove an electron from an atom or molecule
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How can radiation damage living cells?
heating affect can damage skin, ionising radiation can age skin and mutate DNA. Is affected by intensity and duration
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Why can microwaves be used to heat objects containing water?
they are strongly absorbed by water molecules
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How are we protected from microwave radiation?
metal cases and door screens of microwave ovens reflect or absorb microwave radiation
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What do radioactive materials emit all of the time?
ionising gamma radiation
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What does the ozone layer do?
absorbs ultraviolet radiation, emitted by the sun, and producing chemical changes in that part of the atmosphere. Protects living organisms from the harmful effects of ultraviolet radiation
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What is the principle frequency of all objects?
all objects emit electromagnetic radiation with a principle frequency that increases with temperature
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What does the Earth's atmosphere allow?
some electromagnetic radiation emitted by the sun to pass through
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What does radiation do to the Earth's surface?
warms it when absorbed
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what is the greenhouse effect?
radiation emitted by the Earth is absorbed or reflected back by some gases in the atmosphere, keeping the Earth warmer than it otherwise would be
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What are the greenhouse gases in the Earth's atmosphere?
carbon dioxide, methane and water vapour
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What could global warming result in?
impossible to grow some food crops, more extreme weather events and flooding of low lying land because of the rising sea levels
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Why can electromagnetic radiation of some frequencies be used for transmitting information?
some radio and microwaves are not strongly absorbed by the atmosphere, so can be used to carry information for TV and radio. Light and infrared radiation can be used to carry information along optical fibers because it is not significantly absorbed
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What happens to information so it can create a signal?
it can be superimposed to an electromagnetic carrier wave
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Which signal can vary continuously?
analogue signal
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What is a digital signal?
a signal that can only take a small number of discrete values
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How can sound and images be transmitted?
digitally
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What is digital code made up of?
0 and 1
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How can coded information be carried?
switching the electromagnetic carrier wave on and off to create short bursts of waves. 0=no pulse, 1=pulse
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What happens when digital waves are received?
the pulses are decoded to produce a copy of the original sound wave or image
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What is the main advantage of digital signals?
if the original signal has been affected by noise it can be recovered more easily because it only has two states
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What are other advantages of using digital signals?
the information can be stored and processed by computers
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What is the amount of information needed to store an image or sound measured in?
bytes (B)
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Other cards in this set

Card 2

Front

How does a beam of electromagnetic radiation transfer energy?

Back

in 'packets' of energy called photons

Card 3

Front

What does a higher frequency of electromagnetic radiation mean?

Back

Preview of the front of card 3

Card 4

Front

What is the order of the electromagnetic spectrum?

Back

Preview of the front of card 4

Card 5

Front

What speed does electromagnetic radiation travel through a vacuum?

Back

Preview of the front of card 5
View more cards

Comments

LexaBen

Thx. This helps a lot. I can test myself easily now and see whether I understand everything in the module or not.

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