GCSE Physics P2 (OCR)

Question	Answer
Explain how radiation travels.	1) It is emitted by a source. 2) It can be reflected, transmitted or absorbed by materials it encounters. 3) It may effect a detector some distance away when it is absorbed.
How does electromagnetic radiation transfer energy?	In packets called photons.
The ________ the frequency of electromagnetic radiation, the _____ energy is transferred by each photon.	Higher More
List the electromagnetic radiations in order of the energy transferred by each photon.	Radio Waves Microwaves Infrared Visible Light Ultraviolet X-Rays Gamma Rays
How quickly does each type of electromagnetic radiation travel through space?	They all travel at the same speed, 300 000km/s.
What is the intensity of a beam of electromagnetic radiation?	The energy that arrives at a square meter of surface each second.
What is the energy transferred dependent on?	The number of photons arriving and the energy of each photon.
Why does the intensity of a beam of electromagnetic radiation decrease with distance from the source?	Because the radiation spreads out over a wider and wider area, so the surface area it reaches it ever increasing. Also, it is partially absorbed by the medium it travels through.
What is ionisation?	Removing an electron from an atom or molecule, which can initiate chemical reactions.
Which types of electromagnetic radiation are ionising?	Ultraviolet, X-Rays, Gamma Rays.
The _______ ________ of absorbed radiation can damage living cells.	Heating Effect
What issues do some people have with low-intensity microwave radiation.	They think that mobile phones and masts increase health risks because the radiation warms the brain slightly.
Explain how microwaves can be used to heat a potato.	A potato contains water, so it absorbs microwave radiation and vibrates, so its temperature rises.
How are microwave users protected from radiation?	The oven door has a metal grid to reflect the radiation back inside the oven. It has a switch which prevents the oven from operating with its door open.
What do radioactive materials emit?	Ionising gamma radiation all of the time.
What does the ozone layer do?	It absorbs ultraviolet radiation, emitted by the Sun, producing chemical changes in that part of the atmosphere.
How does the ozone layer protect living organisms?	It absorbs some of the radiation which the sun emits.
How can sun creams and clothing protect people against ultraviolet radiation?	They can absorb some of the radiation.
What are the benefits of some physical barriers absorbing some ionising radiation?	X-rays are absorbed by dense materials, so the can produce shadow pictures of bones or of aircraft luggage. Radiographers can be protected by wearing dense materials such as lead and concrete.
All objects emit __________ ________ with a _______ ________ that ________ with ________.	Electromagnetic Radiation Principal Frequency Increases Temperature
The ______ is surrounded by an _______ which......	Earth Atmosphere Allows some of the electromagnetic radiation emitted by the sun to pass through.
What does the electromagnetic radiation do then it is absorbed?	It warms the Earth's surface.
Explain the greenhouse effect.	The radiation emitted by the Earth, which has a lower principal frequency than that emitted by the Sun, is absorbed or reflected back by gases in the Earth's atmosphere; this keeps the Earth warmer than it would otherwise be.
What are some of the greenhouse gasses in the Earth's atmosphere?	Carbon Dioxide Methane Water Vapour
Why, for thousands of years, was the amount of carbon dioxide in the Earth's atmosphere approximately constant?	Plants absorbed carbon dioxide during photosynthesis, then animals and decomposes returned it to the atmosphere during respiration. Humans burned wood, but that was balanced by new trees growing.
Why has the amount of carbon dioxide in the atmosphere been steadily rising over the last two hundred years?	Because fossil fuels are being burned in increasing quantities, which releases the carbon dioxide which was stored in them into the atmosphere. Deforestation releases carbon dioxide and reduces the amount removed by photosynthesis. Methane is produced by grazing animals and rice paddies.
What are computer climate models used for?	Providing evidence that human activities are causing global warming.
What could global warming result in?	- Inability to grow food crops in particular regions. - More extreme weather events due to increased convection and larger amounts of water vapour in the hotter atmosphere. - Flooding of land due to rising sea levels, caused by melting continental ice and thermal expansion of water. - Malaria will spread if mosquitoes can breed in more areas.
Why can electromagnetic radiation of some frequencies be used for transmitting information?	- Some radio waves and microwaves are not strongly absorbed by the atmosphere so can be used to carry information for radio and TV programmes. - Light and infrared can be used to carry information along optical fibres because the radiation travels large distances through glass without being significantly absorbed.
How can a signal be created?	It can be superimposed on to an electromagnetic carrier wave.
What is an analogue signal?	A signal that can vary continuously.
What is a digital signal?	A signal that can only take a small number of discrete values (usually two).
How can sound an images be transmitted?	As a digital signal.
How can digital information be carried?	By switching the electromagnetic carrier wave off and on to create short bursts of waves (pules).
What happens when the waves are received?	They are decoded to produce a copy of the original sound wave or image.
What are the advantage of digital signals over analogue signals?	If the original signal has been affected by noise it can be recovered more easily because the electronic circuit which removes the noise restores it to its nearest value (0 or 1). this is done through a re-generator.
What is measured in Bytes (B)?	The amount of information needed to store an image or sound.
The ______ information stored, the _______ the quality of the sound or image.	More Higher
What are the other advantages of digital signals?	- They can be processed by microprocessors (Phones and PCs) - They can be stored in memories that take up little space - They can carry more information each second than analogue signals - They can be delivered with no loss of quality.

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GCSE Physics P2 (OCR)

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