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P1 Quiz
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Questions in this quiz (64)
1Heat:
- AHeat is a measure of energy
- BWhen a substance is heated, its particles gain kinetic energy (KE). This energy makes the particles in a gas or a liquid move around faster. In a solid, the particles vibrate more rapidly. This is what eventually causes solids to melt and liquids to boil
- CThe energy is measured on an absolute scale. (This means it can't go lower than zero, because there's a limit to how slow particles can move.) The unit of heat energy is the joule (J).
- DHeat is a measure of hotness, the average kinetic energy of the particles in a substance
- EThe energy is not measured on an absolute scale. (This means it can go lower than zero.) The unit of heat energy is the joule (J).
2Temperature is a measure of hotness:
- ATemperature is a measure of the average kinetic energy of the particles in a substance. The hotter something is, the higher its temperature, and the higher the average KE of its particles
- BTemperature is usually measured in °C (degrees Celsius), but there are other temperature scales, like °F (degrees Fahrenheit). These are not absolute scales as they can go below zero
- CEnergy tends to flow from hot objects to cooler ones. If there's a difference in temperature between two places, then energy will flow between them. The greater the difference in temperature, the faster the rate of cooling will be
- DEnergy tends to flow from hot objects to cooler ones. If there's a difference in temperature between two places, then energy will flow between them. The greater the difference in temperature, the slower the rate of cooling will be
- ETemperature is a measure of energy
3Specific Heat Capacity:
- AEnergy = Mass x Specific Heat Capacity x Temperature Change
- BIt takes more heat energy to increase the temperature of some materials than others. Materials which need to gain lots of energy to warm up also release loads of energy when they cool down. They can "store" a lot of heat
- CThe measure of how much energy a substance can store is called its specific heat capacity. Specific heat capacity is the amount of energy needed to raise the temperature of 1 kg of a substance by 1°C
- DWater has a specific heat capacity of 4200 J/kg/°C. This is high. Once water's heated, it stores a lot of energy, which makes it good for central heating systems. Also, water's a liquid so it can easily be pumped around a building
- EEnergy = Mass + Specific Heat Capacity + Temperature Change
- FIt takes more heat energy to increase the temperature of some materials than others. Materials which need to gain lots of energy to warm up don't release loads of energy when they cool down. They can "store" a lot of heat
4Water is good for cooling systems because it can absorb a lot of energy and carry it away.
- ATrue
- BFalse
5You need to put in energy to break intermolecular bonds:
- AWhen you heat a liquid, the heat energy makes the particles move faster. Eventually, when enough particles have enough energy to overcome their attraction to each other, big bubbles of gas form in the liquid - this is boiling
- BWhen you heat a solid, heat energy makes the particles vibrate faster until eventually enough particles have enough energy to overcome their attraction to each other and the particles start to move around - this is melting
- CWhen you heat a liquid, the heat energy makes the particles move faster. Eventually, when enough particles have enough energy to overcome their attraction to each other, big bubbles of gas form in the liquid - this is melting
- DWhen you heat a solid, heat energy makes the particles vibrate faster until eventually enough particles have enough energy to overcome their attraction to each other and the particles start to move around - this is boiling
6Energy is still being used even when temperature stays the same:
- AWhen a substance is melting or boiling, you're still putting in energy, but the energy's used for breaking intermolecular bonds rather than raising the temperature - there are flat spots on the heating graph
- BWhen a substance is condensing or freezing, bonds are forming between particles, which releases energy. This means the temperature doesn't go down until all the substance has turned into a liquid (condensing) or a solid (freezing)
- CWhen a substance is melting or boiling, you're still putting in energy, but the energy's used for making intermolecular bonds rather than raising the temperature - there are flat spots on the heating graph
- DWhen a substance is condensing or freezing, bonds are breaking between particles, which releases energy. This means the temperature doesn't go down until all the substance has turned into a liquid (condensing) or a solid (freezing)
7Specific Latent Heat:
- AThe specific latent heat of melting is the amount of energy needed to melt 1 kg of material without changing its temperature (i.e. the material's got to be at its melting temperature already)
- BThe specific latent heat of boiling is the energy needed to boil 1 kg of material without changing its temperature (i.e. the material's got to be at its boiling temperature already)
- CSpecific latent heat is different for different materials, and it's different for boiling and melting
- DEnergy = Mass x Specific Latent Heat
- EEnergy = Mass / Specific Latent Heat
- FThe specific latent heat of melting is the amount of energy needed to melt 1 kg of material and raise its temperature by 1°C (i.e. the material's got to be at its melting temperature already)
8Conduction occurs mainly in soilds. Conduction of heat is the process where vibrating particles pass on extra kinetic energy to neighbouring particles:
- AIn a solid, the particles are held tightly together. So when one particle vibrates, it bumps into other particles nearby and quickly passes the vibrations on
- BParticles which vibrate faster than others pass on their extra kinetic energy to neighbouring particles. These particles then vibrate faster themselves
- CThis process continues throughout the solid and gradually the extra kinetic energy (or heat) is spread all the way through the solid. This causes a rise in temperature at the other side
- DHouses lose a lot of heat through their windows even when they're shut. Heat flows from the warm inside face of the window to the cold outside face mostly by conduction
- EHouses lose a lot of heat through their windows even when they're shut. Heat flows from the warm inside face of the window to the cold outside face mostly by convection
- FThis process continues throughout the solid and gradually the extra kinetic energy (or heat) is spread all the way through the solid. This causes a fall in temperature at the other side
9Conduction in other materials:
- AMetals conduct heat really well because some of their electrons are free to move. Heating makes the electrons move faster and collide with other free electrons, transferring energy. These then pass on their extra energy to other electrons etc. Because the electrons move freely, this is a much faster way of transferring energy than slowly passing it between jostling neighbouring atoms
- BMost non-metals don't have free electrons, so warm up more slowly, mkaing them good for insulating things - that's why metals are used for saucepans, but non-metals are used for saucepan handles
- CLiquids and gases conduct heat more slowly than solids - the particles aren't held so tightly together, which prevents them bumping into each other so often. So air is a good insulator
- DLiquids and gases conduct heat more slowly than solids - the particles aren't held so tightly together, which prevents them bumping into each other so often. So air is a good conductor
- EMetals conduct heat really well because some of their electrons are free to move. Heating makes the electrons move faster and collide with other free electrons, transferring energy. These then pass on their extra energy to other electrons etc. Because the electrons move freely, this is a much slower way of transferring energy than slowly passing it between jostling neighbouring atoms
10Convection occurs in liquids and gases:
- AConvection occurs when the more energetic particles move from the hotter region to the cooler region - and take their heat energy with them
- BWhen you heat up a liquid or gas, the particles move faster, and the fluid (liquid or gas) expands, becoming less dense. The warmer, less dense fluid rises above its colder, denser surroundings, like a hot air balloon does
- CAs the warm fluid rises, cooler fluid takes its place. As this process continues, you actually end up with a circulation of fluid (convection currents). This is how immersion heaters work
- DConvection can't happen in solids because the particles can't move - they just vibrate on the spot
- EConvection occurs when the more energetic particles move from the cooler region to the hotter region - and take their heat energy with them
- FWhen you heat up a liquid or gas, the particles move faster, and the fluid (liquid or gas) contracts, becoming more dense. The warmer, less dense fluid rises above its colder, denser surroundings, like a hot air balloon does
11Convection in the home:
- AImmersion heaters - as the warm fluid rises, cooler fluid takes its place. As this process continues, you actually end up with a circulation of fluid (convection currents).
- BRadiators - make warm air circulate the room by convection. They heat the air near them and this expands, becomes less dense and rises. The warm air displaces the cooler air and the cool, denser air falls and flows to fill the gap left by the rising heated air
- CRadiators - make warm air circulate the room by convection. They heat the air near them and this expands, becomes less dense and rises. The warm air displaces the cooler air and the cool, denser air falls and flows to fill the gap left by the falling, denser air
- DReducing convection - you need to stop the fluid moving. Clothes, blankets and cavity wall foam insulation all work by trapping pockets of air. The air can't move so the heat has to conduct very slowly through the pockets of air, as well as the material in between (air is a good insulator)
- EReducing convection - you need to stop the fluid moving. Clothes, blankets and cavity wall foam insulation all work by trapping pockets of air. The air can't move so the heat has to conduct very quickly through the pockets of air, as well as the material in between (air is a good conductor)
12If a garden spade is left outside in cold weather, the metal will always feel colder than the wooden handle. But it isn't colder - it just conducts the heat away from your hand quicker. The opposite is true if the spade if left out in the sunshine - it'll feel hotter because it conducts heat into your hand quicker.
- ATrue
- BFalse
13Heat can be transferred as radiation (as well as conduction and convection). Heat is radiated as infrared waves - these are electromagnetic waves that travel in straight lines at the speed of light. Radiation is different from conduction and convection in several ways:
- AIt doesn't need a medium (material) to travel through, so it can occur in a vacuum, like space. This is the only way that heat reaches us from the Sun
- BIt can only occur through transparent substances like air, glass and water
- CThe amount of radiation emitted or absorbed by an object depends to a large extent on its surface colour and texture. This definitely isn't true for conduction and convection
- DIt doesn't need a medium (material) to travel through, so it can occur in a vacuum, like space. This is one way that heat reaches us from the Sun
- EIt can only occur through translucent substances like air, glass and water
14All objects are continually emitting and absorbing heat radiation:
- AThe hotter an object gets, the more heat radiation it emits. Cooler objects will absorb the heat radiation emitted by hotter things, so their temperature increases. For example, you feel heat radiation when the Sun shines on you through a window because you are cooler than the Sun
- BMatt black surfaces are very good absorbers and emitters of radiation
- CLight-coloured, smooth and shiny objects are very poor absorbers and emitters of radiation. They effectively reflect heat radiation - e.g. some people put shiny foil behind their radiators to reflect radiation back into the room rather than heat up the walls
- DThe panels for solar water heating are painted matt black to absorb as much heat as possible and the inner surface is shiny to keep the absorbed heat in
- EThe hotter an object gets, the more heat radiation it emits. Cooler objects will absorb the heat radiation emitted by hotter things, so their temperature decreases. For example, you feel heat radiation when the Sun shines on you through a window because you are cooler than the Sun
- FLight-coloured, smooth and shiny objects are very good absorbers and emitters of radiation. They effectively reflect heat radiation - e.g. some people put shiny foil behind their radiators to reflect radiation back into the room rather than heat up the walls
15Heat radiation is important in cooking:
- AGrills and toasters heat food by infrared (heat) radiation. The heat radiated by a grill is absorbed by the surface particles of the food, increasing their kinetic energy. The heat energy in then conducted or convected to more central parts
- BPeople often line their grill pans with shiny foil. This reflects the heat radiation back onto the bottom of the food being grilled, so the food is cooked more evenly. (It also stops the grill pan getting dirty)
- CMicrowave ovens use radiation to cook food - microwaves are electromagnetic waves that have a different wavelength to infrared. They penetrate about 1 cm into the outer layer of food where they're absorbed by water or fat molecules, increasing their kinetic energy. The energy is then conducted or convected to other parts
- DYou don't cover food with foil in a microwave oven because the microwaves will be reflected away so they won't cook the food, and it can cause dangerous sparks inside the oven. Glass and plastic are okay because the microwaves can pass straight through them
- EMicrowave ovens use radiation to cook food - microwaves are electromagnetic waves that have a different wavelength to infrared. They are absorbed by the surface particles of the food, increasing their kinetic energy. The heat energy in then conducted or convected to more central parts
- FGrills and toasters heat food by infrared (heat) radiation. They penetrate about 1 cm into the outer layer of food where they're absorbed by water or fat molecules, increasing their kinetic energy. The energy is then conducted or convected to other parts
16Thermograms show where your house is leaking heat:
- AA thermogram is a picture taken with a thermal imaging camera
- BObjects at different temperatures emit infrared rays of different wavelengths. The thermogram displays these temperatures as different colours. The hotter parts show up as white, yellow and red, whilst the colder parts are black, dark blue and purple. If something is "hot", it's losing heat
- CObjects at different temperatures emit infrared rays of different wavelengths. The thermogram displays these temperatures as different colours. The hotter parts show up as black, dark blue and purple, whilst the colder parts are white, yellow and red. If something is "hot", it's losing heat
- DA thermogram is a picture taken with a virtual imaging camera
17Energy in the home is emitted and transferred (or wasted) in different areas:
- AThings that emit energy are called sources, e.g. radiators. Things that transfer and waste or lose energy are called sinks, e.g. windows and computers
- BTo save energy, you can insulate your house so the sinks "drain" less energy, e.g. use curtains to reduce energy loss. You can also make sources and sinks more efficient, so they waste less energy, e.g. use energy-saving light bulbs instead of normal ones
- CIt costs money to buy and install insulation, or buy efficient appliances, but it also saves you money, because your energy bills are lower. Eventually, the money you've saved on energy bills will equal the initial cost - the time this takes is called payback time
- DSometimes a cheaper, less energy-saving hot water tank jacket will be better than expensive double glazing because it takes less time to actually save money - payback time = initial cost / annual saving
- ESometimes a cheaper, less energy-saving hot water tank jacket will be better than expensive double glazing because it takes less time to actually save money - payback time = annual saving / initial cost
- FTo save energy, you can insulate your house so the sinks "drain" less energy, e.g. use curtains to reduce energy loss. You can also make sources and sinks more efficient, so they waste more energy, e.g. use energy-saving light bulbs instead of normal ones
18Insulation:
- ALoft insulation - fibreglass "wool" laid across the loft floor reduces conduction through the ceiling into the roof space
- BHot water tank jacket - reduces convection
- CCavity walls and insulation - two layers of bricks with a gap between them reduce conduction but you still get some energy lost by convection. Squirting insulating foam into the gap traps pockets of air to minimise this convection (heat is still lost through the walls by radiation though)
- DDouble glazing - two layers of glass with an air gap between reduce conduction
- EDraught-proofing - strips of foam and plastic around doors and windows stop hot air going out - reducing convection
- FThick curtains - reduce convection and radiation through the windows
19Machines always waste some energy:
- AUseful machines are only useful because they convert energy from one form to another e.g. car engines convert chemical energy (petrol or diesel) into kinetic (movement) energy
- BThe total energy output is always the same as the total energy input, but only some of the output energy is useful. So for every joule of chemical energy put into a car engine, only a fraction of it will be converted into useful kinetic energy
- CThis is because some of the input energy is always lost or wasted, often as heat. For a car engine, lots of energy is wasted as heat and sound energy
- DThe less energy that is wasted, the more efficient the device is said to be
- EThe more energy that is wasted, the more efficient the device is said to be
- FThe total energy output is not always the same as the total energy input, but only some of the output energy is useful. So for every joule of chemical energy put into a car engine, only a fraction of it will be converted into useful kinetic energy
20More efficient machines waste less energy:
- AEfficiency = useful energy output / total energy input (x 100%)
- BEfficiency = useful energy output x total energy input (x 100%)
- CEfficiency can also be shown on a Sankey diagram
- DEfficiency can also be shown on a Swankey diagram
- EEfficiency will be between 0 and 1 or 0% and 100%. The higher the number the more efficient the machine is
- FEfficiency will be between 0 and 1 or 0% and 100%. The lower the number the more efficient the machine is
21Sankey diagrams:
- ASankey diagrams are just energy transformation diagrams - they make it easy to see at a glance how much of the input energy is being usefully employed compared with how much is being wasted
- BThe thicker the arrow, the more energy it represents - so you see a big thick arrow going in, then several smaller arrows going off it to show the different energy transformations taking place
- CYou can have either a little sketch or a properly detailed diagram where the width of each arrow is proportional to the number of joules it represents
- DYou can have either a little sketch or a properly detailed diagram where the width of each arrow is inversely proportional to the number of joules it represents
- EThe thinner the arrow, the more energy it represents - so you see a big thick arrow going in, then several smaller arrows going off it to show the different energy transformations taking place
22What is the efficiency of this lightbulb?
- A10 / 100 = 0.1 or 10%
- B90 / 100 = 0.9 or 90%
- C10 / 90 = 0.11 or 11%
23Waves have amplitude, wavelength and frequency:
- AAmplitude - the displacement from the rest position to a crest
- BWavelength - the length of a full cycle of the wave, e.g. from crest to crest
- CFrequency - the number of complete cycles or oscillations passing a certain point per second. Frequency is measured in hertz (Hz). 1 Hz is 1 wave per second
- DAmplitude - the displacement from a trough to a crest
- EWavelength - the length of a half cycle of the wave, e.g. from crest to crest
- FFrequency - the number of complete cycles or oscillations passing a certain point per minute. Frequency is measured in hertz (Hz). 1 Hz is 1 wave per second
24What is the equation for wave speed?
- ASpeed (m/s) = Frequency (Hz) x Wavelength (m)
- BSpeed (m/s) = Frequency (Hz) / Wavelength (m)
- CSpeed (m/s) = Frequency (Hz) x Amplitude (m)
25This means wavelength (Greek letter "lambda").
- ATrue
- BFalse
26Converting units:
- AThe standard (SI) units involved in wave equations are: metres, seconds, m/s and hertz (Hz)
- B1 kHz (kilohertz) = 1000 Hz
- C1 MHz (1 megahertz) = 1 000 000 Hz
- DWavelengths can also be given in other units, e.g. km for long-wave radio
- EThe standard (SI) units involved in wave equations are: kilometres, hours, km/h and hertz (Hz)
- F1 MHz (1 megahertz) = 1 000 000 000 Hz
27All waves can be reflected, refracted and diffracted:
- AWaves travel in a straight line through whatever substance they're travelling in
- BWhen waves arrive at an obstacle (or meet a new material), their direction of travel can be changed
- CWaves can change direction by reflection, refraction or diffraction
- DWhen waves arrive at an obstacle (or meet a new material), their direction of travel is never changed
- EWaves travel at right angles to whatever substance they're travelling in
28Reflection of light lets us see things:
- AReflection of light is what allows us to see objects. Light bounces off them into our eyes
- BWhen a beam of light reflects from an uneven surface such as a piece of paper, the light reflects off at different angles
- CWhen a beam of light reflects from an even surface (smooth and shiny like a plane mirror) then it's all reflected at the same angle and you get a clear reflection
- DThe law of reflection applies to every reflected ray: Angle of Incidence = Angle of Reflection. These two angles are always defined between the ray itself and the normal (an imaginary line that's perpendicular to the surface at the point of incidence where the light hits the surface)
- EThe law of reflection applies to every reflected ray: Angle of Incidence = Angle of Reflection. These two angles are sometimes defined between the ray itself and the normal (an imaginary line that's perpendicular to the surface at the point of incidence where the light hits the surface)
- FWhen a beam of light reflects from an even surface (smooth and shiny like a plane mirror) then it's all reflected at slightly different angles and you get a clear reflection
29Total internal reflection depends on the critical angle:
- AA wave hitting a surface can experience total internal reflection. This can only happen when the light ray travels through a dense material like glass, water or Perspex towards a less dense substance like air
- BA wave hitting a surface can experience total internal reflection. This can only happen when the light ray travels through a less dense substance like air towards a dense material like glass, water or Perspex
- CIf the angle of incidence is big enough, the ray doesn't come out at all, but reflects back into the material. Big enough means bigger than the critical angle for that particular material - every material has its own, different critical angle
- DIf the angle of incidence is less than the critical angle most of the light is refracted into the outer layer, but some of it is internally reflected. If it is equal to the critical angle the ray would go along the surface (with quite a bit of internal reflection as well). If it is greater than the critical angle no light comes out. It's all internally reflected, i.e. total internal reflection
- EIf the angle of incidence is less than the critical angle most of the light is refracted into the outer layer, but some of it is internally refracted. If it is equal to the critical angle the ray would go along the surface (with quite a bit of internal reflection as well). If it is greater than the critical angle no light comes out. It's all internally reflected, i.e. total internal reflection
- FIf the angle of incidence is big enough, the ray doesn't come out at all, but reflects back into the material. Big enough means bigger than the critical angle for that particular material - every material has the same critical angle
30Waves travel at different speeds in substances which have different densities. So when a wave crosses a boundary between two substances (e.g. from glass to air) it changes speed:
- AIf a light wave hits the boundary "face on", it slows down but carries on in the same direction. It now has a shorter wavelength but the same frequency (it's gone from a less dense material to a more dense material)
- BIf a wave meets a different medium at an angle, part of the wave hits the denser layer first and slows down while another part carries on at the first, faster speed for a while. So the wave changes direction - it's been refracted
- CWhen light passes from air into the glass of a window pane (a denser medium), it slows down - causing the light to refract towards the normal. When the light reaches the "glass to air" boundary on the other side of the window, it speeds up and refracts away from the normal
- DWaves are only refracted if they meet a new medium at an angle. If they're travelling along the normal (i.e. the angle of incidence is zero) they will change speed, but are not refracted - they don't change direction
- EWhen light passes from air into the glass of a window pane (a denser medium), it slows down - causing the light to refract away from normal. When the light reaches the "glass to air" boundary on the other side of the window, it speeds up and refracts towards the normal
- FWaves are only refracted if they meet a new medium at an angle. If they're travelling along the normal (i.e. the angle of incidence is zero) they will change speed and are refracted - they change direction
31All waves spread out (diffract) at the edges when they pass through a gap or pass an object:
- AThe amount of diffraction depends on the size of the gap relative to the wavelength of the wave. The narrower the gap, or the longer the wavelength, the more the wave spreads out. A narrow gap is one about the same size as the wavelength of the wave
- BLight has a very small wavelength (about 0.0005 mm), so it can be diffracted but it needs a really small gap. You can't see someone through an open door unless you're directly facing the door because the gap is about a million times bigger than the wavelength of light, so it won't diffract enough
- CYou can hear someone through an open door even if you can't see them, because the size of the gap and the wavelength of sound are roughly equal, causing the sound wave to diffract and fill the room
- DIf a gap is about the same size as the wavelength of a light, you can get a diffraction pattern of light and dark fringes. You can also get diffraction around the edges of obstacles too. The shadow is where the wave is blocked. The wider the obstacle compared to the wavelength, the less diffraction it causes, so the longer the shadow
- EIf a gap is about the same size as the wavelength of a light, you can get a diffraction pattern of light and dark fringes. You can also get diffraction around the edges of obstacles too. The shadow is where the wave is blocked. The wider the obstacle compared to the wavelength, the more diffraction it causes, so the longer the shadow
- FThe amount of diffraction depends on the size of the gap relative to the wavelength of the wave. The narrower the gap, or the longer the wavelength, the more the wave spreads out. A narrow gap is one that is smaller than the wavelength of the wave
32There are seven types of electromagnetic (EM) wave:
- AElectromagnetic radiation can occur at many different wavelengths. There is a continuous spectrum of different wavelengths, but waves with similar wavelengths tend to have similar properties
- BAll forms of electromagnetic radiation travel at the same speed through a vacuum. This means that waves with a shorter wavelenth have a higher frequency
- CIn order of increasing frequency and decreasing wavelength - radio waves, microwaves, infrared, visible light, ultra violet, X-rays, gamma rays
- DIn order of increasing frequency and decreasing wavelength - radio waves, microwaves, visible light, infrared, ultraviolet, X-rays, gamma rays
- EAbout half the EM radiation we receive from the Sun is visible light. Most of the rest is infrared (heat), with some UV (ultraviolet). UV is what gives us a suntan
- FAll forms of electromagnetic radiation travel at the same speed through a vacuum. This means that waves with a shorter wavelenth have a lower frequency
33The properties of EM waves depend on frequency and wavelength:
- AAs the frequency and wavelength of EM radiation changes, its interaction with matter changes - i.e. the way a wave is absorbed, reflected or transmitted by any given substance changes
- BAs a rule, the EM waves at each end of the spectrum tend to be able to pass through material, whilst those nearer the middle are absorbed
- CEM waves with higher frequency (shorter wavelength), like X-rays, tend to be more dangerous to living cells. That's because they have more energy
- DWhen any EM radiation is absorbed it can cause heating and ionisation (if the frequency is high enough). Ionisation is where an atom or molecule either loses or gains electrons and it can be dangerous
- EAs the frequency and wavelength of EM radiation changes, its interaction with matter stays the same - i.e. the way a wave is absorbed, reflected or transmitted by any given substance stays the same
- FAs a rule, the EM waves at each end of the spectrum are absorbed, whilst those nearer the middle tend to be able to pass through material
34As well as cooking our food and keeping us warm, EM waves are used for communication. E.g. radio waves are used for radio, microwaves for mobile phones etc. Before you communicate information though, it's changed into an electrical signal, which is then sent off on its own (like you get in an ordinary phone line) or carried on an EM wave. The different types of signals have advantages and disadvantages:
- AUsing light, radio and electrical signals is great because the signals travel really fast. Electrical wires and optical fibres can carry loads of information very quickly
- BInformation sent through optical fibres and electrical wires is pretty secure - they're inside a cable and so can't easily be tapped in to. Radio signals travel through the air, so they can be intercepted more easily. This is an issue for people using wireless internet networks
- CCables can be difficult to repair if they get broken, which isn't a problem for wireless methods
- DWireless communication is portable (e.g. mobile phones, laptop wi-fi etc.). It does rely on an aerial to pick up a signal though, and signal strength often depends on location
- ECables are easy to repair if they get broken, which is a problem for wireless methods
- FInformation sent through optical fibres and electrical wires is pretty secure - they're inside a cable and so can easily be tapped in to. Radio signals travel through the air, so they can't be intercepted as easily. This is an issue for people using wireless internet networks
35Communicating with light can require a code:
- AHistorically, light was used to speed up communication over long distances. By creating a code of "on-off" signals, a message could be relayed between stations far away, by flashing a light on and off in a way that could be decoded. This is the principle behind the Morse code
- BIn Morse code, each letter of the alphabet (and each number 0-9) is represented by a sequence of "dots" and "dashes" - which are pulses of light (or sound) that last for a certain length of time e.g. in the International Morse Code SOS is . . . _ _ _ . . .
- CThe Morse code is a type of digital signal because the light pulse is either "on" or "off"
- DThe Morse code is a type of analogue signal because the light pulse is either "on" or "off"
- EIn Morse code, each letter of the alphabet (and each number 0-9) is represented by a sequence of "dots" and "dashes" - which are pulses of infrared (or sound) that last for a certain length of time e.g. in the International Morse Code SOS is . . . _ _ _ . . .
36Light signals can travel through optical fibres:
- AA more modern use of light for communication is the use of optical fibres, which can carry data over long distances as pulses of light or infrared radiation. They work by bouncing waves off the sides of a very narrow core which is protected by outer layers
- BThe ray of light enters the fibre so that it hits the boundary between the core and the outer cladding at an angle greater than the critical angle for the material. This causes total internal reflection of the ray within the core - the pulse of light enters at one end and is reflected over and over again until it emerges at the other end
- COptical fibres are increasingly being used for telephone and broadband internet cables, replacing the old electrical ones. They're also used for medical purposes - to "see inside" the body without having to operate. They are most commonly seen as twinkly lights
- DA more modern use of light for communication is the use of optical fibres, which can carry data over short distances as pulses of light or infrared radiation. They work by bouncing waves off the sides of a very narrow core which is protected by outer layers
- EThe ray of light enters the fibre so that it hits the boundary between the core and the outer cladding at an angle less than the critical angle for the material. This causes total internal reflection of the ray within the core - the pulse of light enters at one end and is reflected over and over again until it emerges at the other end
37Using light for communication has lots of advantages:
- AUsing light is a very quick way to communicate. In a vacuum, light travels at 300 000 000 m/s - it can't travel that fast through optical fibres (it's slowed down by about 30%) but it's still pretty quick
- BMultiplexing means that lots of different signals can be transmitted down a single optical fibre at the same time, so you don't need as many cables
- CAs light is used as a "digital" signal, there's little interference
- DUsing light is a very quick way to communicate. In a vacuum, light travels at 900 000 000 m/s - it can't travel that fast through optical fibres (it's slowed down by about 30%) but it's still pretty quick
- EMultiplexing means that lots of different signals can be transmitted down a single optical fibre at the same time, so you need more cables
38Ordinary visible light is a combination of waves of different frequency and wavelength (and so colour) that are “out of phase” with each other (i.e. the crests and troughs don’t match). Lasers are just a special type of visible light. They produce narrow, intense beams of monochromatic light:
- AAll the waves in a laser beam are at the same frequency (and wavelength). This makes the light monochromatic - it’s all one single, pure colour
- BThe light waves are all in phase with each other - the troughs and crests line up, increasing the amplitude, so producing an intense beam. The waves are said to be coherent because they have an unfixed phase difference (in this case zero, i.e. the waves are “in phase”)
- CLasers have a low divergence - the beam is narrow, and it stays narrow, even at a long distance from the light source (it doesn’t diverge)
- DLasers have a high divergence - the beam is narrow, and it stays narrow, even at a long distance from the light source (it doesn’t diverge)
- EThe light waves are all in phase with each other - the troughs and crests line up, increasing the amplitude, so producing an intense beam. The waves are said to be coherent because they have a fixed phase difference (in this case zero, i.e. the waves are “in phase”)
- FAll the waves in a laser beam are at the same frequency (but different wavelength). This makes the light monochromatic - it’s all one single, pure colour
- AAll the waves in a laser beam are at the same frequency (and wavelength). This makes the light monochromatic - it’s all one single, pure colour
39Why do long wavelengths travel well through Earth's atmosphere?
- ARadio waves and microwaves are good at transferring information over long distances. This is because they don't get absorbed by the Earth's atmosphere as much as waves in the middle of the EM spectrum (e.g. heat/IR), or those at the high-frequency end of the spectrum (e.g. gamma or X-rays). You couldn't use high-frequency waves anyway - they'd be far too powerful
- BRadio waves and microwaves are good at transferring information over long distances. This is because they don't get absorbed by the Earth's atmosphere as much as waves in the middle of the EM spectrum (e.g. heat/IR), or those at the high-frequency end of the spectrum (e.g. gamma or X-rays). You couldn't use high-frequency waves anyway - they'd be far too dangerous
40Radio waves are used mainly for communications. They are EM radiation with wavelengths longer than about 10 cm. Different wavelengths of radio wave refract and diffract in different ways:
- ALong-wave radio (wavelengths of 1-10 km) can be transmitted from one place and received halfway round the world because they diffract (bend) around the curved surface of the Earth
- BRadio waves used for TV and FM radio transmissions have very short wavelengths (10 cm - 10 m). To get reception, you must be in direct sight of the transmitter - the signal doesn't bend around hills or travel far through buildings
- CShort-wave radio signals with wavelengths of about 10 m - 100 m can be received at long distances from the transmitter because of reflection in the ionosphere. Medium-wave signals (the shorter ones anyway) can also reflect from the ionosphere, depending on the atmospheric conditions and time of day
- DLong-wave radio signals with wavelengths of about 1-10 km can be received at long distances from the transmitter because of reflection in the ionosphere. Medium-wave signals (the shorter ones anyway) can also reflect from the ionosphere, depending on the atmospheric conditions and time of day
- EShort-wave radio (wavelengths of 10 m -100 m) can be transmitted from one place and received halfway round the world because they diffract (bend) around the curved surface of the Earth
41Diffraction is when waves spread out at the edges when they pass through a gap or past an object. The amount of diffraction depends on the wavelength of the wave, relative to the size of the gap or obstacle. Diffraction makes a difference to signal strength:
- ALonger wavelengths can encounter a lot of diffraction because they are large compared with the gap or obstacle. This means that they are able to bend around corners and any obstacles- such as hills, tall buildings etc.
- BSo longer wavelength radio waves can travel long distances between the transmitter and receiver without them having to to be in line of sight of each other. Shorter wavelength radio waves and microwaves don't diffract very much, so the transmitters need to be located high up to avoid obstacles (and even then they can only cover short distances)
- CSome areas have trouble receiving shorter wavelength radio (and microwave) signals - e.g. if you live at the foot of a mountain you will probably have poor signal strength
- DDiffraction can also occur at the edges of the dishes used to transmit signals. This results in signal loss - the wave is more spread out so the signal is weaker
- ESo longer wavelength radio waves can travel long distances between the transmitter and receiver without them having to to be in line of sight of each other. Shorter wavelength radio waves and microwaves don't diffract very much, so the transmitters need to be located low down to avoid obstacles (and even then they can only cover short distances)
- FDiffraction can also occur at the edges of the dishes used to transmit signals. This results in signal loss - the wave is less spread out so the signal is weaker
42Lasers are useful in lots of areas - manufacturing, surgery, dentistry, weaponry and CD players which use lasers to read digital information:
- AThe surface of a CD has a pattern of billion of shallow pits cut into it. The areas between the pits are called lands (although the laser shines from underneath, so it sees the pits as slightly raised areas)
- BA laser shone onto the CD is reflected from the shiny bottom surface as it spins around in the player. The beam is reflected from a land and a pit slightly differently - and this difference can be picked up by a light sensor. These differences in reflected signals can then be changed into an electrical signal
- CThe pits and lands themselves don’t represent the digital ons and offs. It’s actually a change in the reflected beam which represents on, while no change represents off
- DAn amplifier and a loudspeaker then convert the electrical signal into sound of the right pitch (frequency) and loudness
- EA laser shone onto the CD is reflected from the shiny bottom surface as it spins around in the player. The beam is reflected from a land and a pit the same - and this difference can be picked up by a light sensor. These differences in reflected signals can then be changed into an electrical signal
- FThe pits and lands themselves represent the digital ons and offs. It’s actually a change in the reflected beam which represents on, while no change represents off
43Infrared has many uses around the home:
- AInfrared radiation can be used in cooking, e.g. in grills and toasters
- BRemote controls transfer information to TVs and DVD players using infrared radiation
- CInfrared radiation can be used to transmit information between mobile phones or computers - but only over short distances
- DInfrared sensors are used in security systems, e.g. burglar alarms and security lights. These sensors detect heat from an intruder’s body
- EInfrared can also be used instead of ultraviolet to carry information through optical fibres
- FInfrared radiation can be used to transmit information between mobile phones or computers - but only over long distances
44Infrared radiation can be used to monitor temperature:
- AInfrared radiation is also known as heat radiation. It’s given out by hot objects - the hotter the object, the more IR radiation it gives out
- BThis means infrared can be used to monitor temperatures. For example, heat loss through a house’s uninsulated roof can be detected using infrared sensors
- CInfrared is also detected by night-vision equipment. The equipment turns it into an electrical signal, which is displayed on a screen as a picture. The hotter an object is, the brighter it appears. Police and the military use this to spot criminals running away
- DThis means infrared can be used to monitor temperatures. For example, heat loss through a house’s uninsulated roof can be detected using light sensors
- EInfrared is also detected by night-vision equipment. The equipment turns it into a digital signal, which is displayed on a screen as a picture. The hotter an object is, the brighter it appears. Police and the military use this to spot criminals running away
45Infrared signals can control electrical equipment:
- ARemote controls emit pulses of IR to control electrical devices such as TVs or DVD players. If it was visible, you’d see it flickering when you pressed a button on the control. The pulses act as a digital (“on/off”) code - similar to how Morse code works
- BThe device will detect and decode the pattern of pulses coming from the remote control and follow the coded instruction. E.g. a CD player might be programmed to know that a certain sequence of pulses at a particular speed means “play”, so when it receives this signal it will play the CD
- CInfrared signals are used in the same way to transfer information between mobile phones and computers over short distances (so they’re another form of wireless communication)
- DRemote controls emit pulses of IR to control electrical devices such as TVs or DVD players. If it was visible, you’d see it flickering when you pressed a button on the control. The pulses act as an analogue code - similar to how Morse code works
- EThe device will detect and decode the pattern of pulses coming from the remote control and follow the coded instruction. E.g. a CD player might be programmed to know that a certain sequence of pulses at a particular amplitude means “play”, so when it receives this signal it will play the CD
46Drawbacks of infrared radiation:
- AYou need to be close to the device you’re operating, because the IR beam from a small, low-powered remote control is fairly weak
- BYou need to point the beam straight at the detector on the device, because the IR waves only travel in a straight line
- CSome remote controls, such as the ones on electronic car keys, use radio waves rather than IR. The radio waves can bend (diffract) - that’s why you can open the car without pointing it at it
- DYou need to be close to the device you’re operating, because the IR beam from a small, low-powered remote control is very strong
- EYou need to point the beam straight at the detector on the device, because the IR waves diffract too much
47When a wave comes up against something that has a different density, it changes speed. If the wave hits the new substance at an angle, it changes direction. This is refraction. When it happens high up in the atmosphere, it can help waves travel further for long distance communication:
- AUV radiation from the Sun creates layers of ionised atoms (atoms that have either gained or lost electrons) in the Earth's atmosphere. These electrically charged layers are called the ionosphere
- BRadio waves travel faster through ionised parts of the atmosphere than non-ionised parts. This causes refraction. Short-wave (10 m - 100m) and medium wave (about 300 m) radio signals are refracted most in the ionosphere - they are effectively bounced back of reflected back to Earth. This means short- and medium-wave radio signals can be received a long way from the transmitter
- CThe amount a wave is refracted in the ionosphere depends on its frequency and angle of elevation. High frequency / short wavelength signals such as short-wave radio don't refract as much as medium-wave. E.g. waves with a higher frequency or transmitted at a higher angle of elevation are gradually refracted back to Earth whereas lower frequency waves or ones transmitted at a lower angle of elevation are refracted back very quickly
- DRadio waves "bounce" off the ionosphere in a similar way to how light waves totally internally reflect inside optical fibres. Refraction's not always good though. It can disrupt a signal by bending it away from the receiver dish
- EThe amount a wave is refracted in the ionosphere depends on its frequency and angle of elevation. High frequency / short wavelength signals such as short-wave radio don't refract as much as medium-wave. E.g. waves with a higher frequency or transmitted at a higher angle of elevation are very quickly refracted back to Earth whereas lower frequency waves or ones transmitted at a lower angle of elevation are refracted back gradually
- FRadio waves travel faster through ionised parts of the atmosphere than non-ionised parts. This causes refraction. Short-wave (10 m - 100m) and medium wave (about 300 m) radio signals are refracted most in the ionosphere - they are effectively bounced back of reflected back to Earth. This means short- and medium-wave radio signals can only be received if they are in the line of sight of the transmitter
48There's a limited number of radio frequencies that can be used too transmit a good analogue signal - so radio stations often broadcast using waves of very similar frequencies. These analogue signals often suffer from interference because of this - similar waves covering a similar area can combine, which causes "noise". This is why radio stations near to each other use different frequencies - so they don't interfere as much:
- ADigital Audio Broadcasting (DAB) works in a different way to traditional radio broadcasts - it's digital instead of analogue to start with. With DAB, many different signals are compressed, then transmitted as a single wave - this is known as multiplexing
- BThe compressed waves are transmitted across a relatively small frequency bandwidth and separated out by the receivers at the other end. You need a DAB radio set to pick up and decode the signals
- CDAB suffers less interference than traditional radio broadcasts, and since the signals from many stations can be broadcast at the same frequency (multiplexing), it means an increase in the potential number of radio stations available
- DAt the moment there are a limited number of DAB transmitters in the UK (and the world) so some areas can't receive digital radio signals at all. Even if you can receive DAB, the sound quality is often not as good as a traditional FM radio broadcast, due to the compression of the signal
- EDigital Audio Broadcasting (DAB) works in a different way to traditional radio broadcasts - it's digital instead of analogue to start with. With DAB, many different signals are compressed, then transmitted as many waves - this is known as multiplexing
- FDAB suffers less interference than traditional radio broadcasts, and since the signals from many stations can be broadcast at the same frequency (multiplexing), it means an decrease in the potential number of radio stations available
49Microwaves are used for satellite communication:
- ACommunication to and from satellites (including satellite TV signals and satellite phones) uses microwaves. But you need to use wavelengths which can pass easily through the Earth's watery atmosphere without too much absorption
- BFor satellite TV and phones, the signal from a transmitter is transmitted into space where it's picked up by the satellite's receiver dish orbiting thousands of kilometres above the Earth. The satellite transmits the signal back to Earth in a different direction where it's received by a satellite dish on the ground
- CMicrowaves are also used by remote-sensing satellites - to "see" through the clouds and monitor oil spills, track the movement of icebergs, see how much rainforest has been chopped down and so on
- DCommunication to and from satellites (including satellite TV signals and satellite phones) uses microwaves. But you need to use wavelengths which can pass easily through the Earth's watery atmosphere without too much reflection
- EFor satellite TV and phones, the signal from a transmitter is transmitted into space where it's picked up by the satellite's receiver dish orbiting thousands of kilometres above the Earth. The satellite transmits the signal back to Earth in the same direction where it's received by a satellite dish on the ground
50Mobile phone calls travel as microwaves from your phone to the nearest transmitter (or mast). The transmitters pass signals between each other, then back to your mobile phone:
- AMicrowaves have a shorter wavelength than radio waves, so they don't diffract much. This means they're affected by the curvature of the Earth because they don't bend round it like long-wave radio waves. It also means they're blocked more by large obstacles like hills because they can't bend round them
- BThis means that microwave transmitters need to be positioned in line of sight - they're usually high up on hilltops so they can "see each other", and they're positioned fairly close together. If there's a hill or a man-made obstacle between your phone and the transmitter, you'll probably get a poor signal, or no signal at all
- CThe microwave frequencies used are partially absorbed by water, even though they can pass through the atmosphere. So in adverse weather (or if there's a lake nearby) there can be some signal loss through absorption or scattering. This is why you can lose satellite TV signal in a storm. Sometimes there's interference between signals, which can also affect signal strength
- DThis means that microwave transmitters need to be positioned in line of sight - they're usually high up on hilltops so they can "see each other", and they're positioned fairly close together. If there's a hill or a man-made obstacle between your phone and the transmitter, you'll probably get a good signal, or no signal at all
- EThe microwave frequencies used are completely absorbed by water, even though they can pass through the atmosphere. So in adverse weather (or if there's a lake nearby) there can be some signal loss through absorption or scattering. This is why you can lose satellite TV signal in a storm. Sometimes there's interference between signals, which can also affect signal strength
51Mobile masts may be dangerous - but there's conflicting evidence:
- AMicrowaves used for communications need to pass through the Earth's watery atmosphere, but the microwaves used in microwave ovens have a different wavelength - they're actually absorbed by the water molecules in the food. It's the absorption that's harmful - if microwaves are absorbed by water molecules in living tissue, cells may be burned or killed
- BSome people think that the microwaves emitted into your body from using a mobile phone or living near a mobile phone mast could damage your health. There's no conclusive proof either way yet though. Lots of studies have been published, which has allowed the results to be checked, but so far they have given conflicting evidence
- CAny potential dangers would be increased by prolonged exposure - e.g. living close to a mast or using your mobile phone all the time. This means we have to carefully balance the potential risks and the benefits of this technology until we know more - in terms of where we locate masts and how much we choose to use our mobile phones
- DMicrowaves used for communications need to pass through the Earth's watery atmosphere, but the microwaves used in microwave ovens have the same wavelength - they're actually absorbed by the water molecules in the food. It's the absorption that's harmful - if microwaves are absorbed by water molecules in living tissue, cells may be burned or killed
- ESome people think that the microwaves emitted into your body from using a mobile phone or living near a mobile phone mast could damage your health. There's no conclusive proof either way yet though. Some studies have been published, which has allowed the results to be checked, but so far they have given conflicting evidence
- FAny potential dangers would be increased by shorter exposure - e.g. living close to a mast or using your mobile phone all the time. This means we have to carefully balance the potential risks and the benefits of this technology until we know more - in terms of where we locate masts and how much we choose to use our mobile phones
52We use different receivers (sensors) to pick up the different types of EM waves used for communication - e.g. telescopes, satellite dishes, microscopes etc. The size of the receiver depends on the size of the wave:
- AThe minimum size of receiver needed is linked to the size of the wavelength of the wave - the longer the wavelength, the larger the receiver should be. So radio waves need the biggest receivers, then microwaves, then infrared, then light waves etc.
- BThis is because of diffraction - when a wave enters a receiver it passes through a gap. If the wave is diffracted, it spreads out and you lose detail. The amount of diffraction is affected by the size of the gap compared to the wavelength - gaps about the same size as the wavelength cause lots of diffraction, but as the gap size increases there is less diffraction
- CSo the bigger the receiver compared with the wavelength of wave being received, the less diffraction it causes, so the clearer the information received is
- DThe maximum size of receiver needed is linked to the size of the wavelength of the wave - the longer the wavelength, the larger the receiver should be. So radio waves need the biggest receivers, then microwaves, then infrared, then light waves etc.
- EThis is because of diffraction - when a wave enters a receiver it passes through a gap. If the wave is diffracted, it spreads out and you lose detail. The amount of diffraction is affected by the size of the gap compared to the wavelength - gaps smaller than the wavelength cause lots of diffraction, but as the gap size increases there is less diffraction
- FSo the bigger the receiver compared with the wavelength of wave being received, the less diffraction it causes, so the less clear the information received is
53Telescopes help you see distant objects clearer - e.g. astronomers look for very distant stars and galaxies using them. Different telescopes are used to collect different EM waves - e.g. optical telescopes receive visible light, radio telescopes collect radio waves etc. :
- ABigger telescopes give us better resolution (i.e. lots of detail) because they cause less diffraction, so the information is clearer. Telescopes with small gaps compared to the wavelength they're looking for have limited resolving power - they are said to be diffraction-limited
- BLight waves have a relatively small wavelength compared to radio waves. Since radio waves can be more than 10 000 000 000 times bigger than light waves, this would mean having a ridiculously big receiver (about the size of the UK for a decent one). So we just make do with lower resolution (although the dishes are still pretty huge)
- CTo get a higher resolution, radio telescopes are often linked together and their signals combined to get more detailed information - acting like a single giant receiver. A bigger receiver can also collect more EM waves, giving a more intense image - so a bigger telescope can observe fainter objects
- DRadio telescopes are often made of mesh rather than solid metal - the waves are so big they won't go through the gaps - making it cheaper to make bigger dishes
- ETo get a lower resolution, radio telescopes are often linked together and their signals combined to get more detailed information - acting like a single giant receiver. A bigger receiver can also collect more EM waves, giving a more intense image - so a bigger telescope can observe fainter objects
- FBigger telescopes give us better resolution (i.e. lots of detail) because they cause less diffraction, so the information is clearer. Telescopes with small gaps compared to the wavelength they're looking for have limited resolving power - they are said to be diffraction-affected
54Optical microscopes are diffraction limited:
- AOptical microscopes have to be small, because you usually use them to look at small samples of tiny things in the lab - you want to collect light coming from a very small area only
- BTheir small size makes it hard to get a good resolution - the gap needs to be really small, so you still get some diffraction even though light has a small wavelength
- COptical microscopes have to be small, because you usually use them to look at small samples of tiny things in the lab - you want to collect light coming from a very small area and a large area
- DTheir small size makes it easy to get a good resolution - the gap needs to be really small, but you don't get any diffraction because light has such a small wavelength
55To communicate any kind of information (e.g. sound, pictures), it needs to be converted into electrical signals before it's transmitted:
- AThe electrical signals can then be sent long distances down telephone wires or carried on EM waves. The signals can either be analogue or digital
- BAn analogue signal can take any value within a certain range. The amplitude and frequency of an analogue wave vary continuously
- CA digital signal can only take two values. These values tend to be called on/off, or 1/0. For example, you can send data along optical fibres as short pulses of light
- DA digital signal can take any value within a certain range. The amplitude and frequency of an analogue wave vary continuously
- EAn analogue signal can only take two values. These values tend to be called on/off, or 1/0. For example, you can send data along optical fibres as short pulses of light
56Digital signals have advantages over analogue:
- ADigital and analogue signals weaken as they travel, so they might need to be amplified along their route. They also pick up interference or noise from electrical disturbances or other signals
- BWhen you amplify an analogue signal, the noise is amplified too - so every time it's amplified, the signal loses quality. The noise is easier to remove or ignore with digital, so the signal remains high quality - it's easier to distinguish between two values than any values within a certain range
- CWith digital technology you can transmit several signals at the same time using just one cable or EM wave - this is called multiplexing
- DThe advantages of digital signals over analogue have played a big part in the "switching over" from analogue to digital TV and radio broadcasts
- EWhen you amplify an analogue signal, the noise is amplified too - so every time it's amplified, the signal loses quality. The noise is harder to remove or ignore with digital, so the signal remains high quality - it's easier to distinguish between two values than any values within a certain range
- FDigital and analogue signals strengthen as they travel, so they might need to be amplified along their route. They also pick up interference or noise from electrical disturbances or other signals
57What is interference?
- AWhen two or more waves of a similar frequency meet, they can create one combined signal with a new amplitude. This is called interference. You get it when two radio stations transmit on similar frequencies
- BWhen two or more waves of a similar frequency meet, they can create one combined signal with a new amplitude. This is called interference. You get it when two radio stations transmit on different frequencies
58Multiplexing happens in phone wires:
- AWhen you're on the phone, your voice is converted into a digital signal and transmitted regularly at very small time intervals. In between your voice signals being transmitted, thousands of other people's voice signals can be slotted in or "multiplexed". The samples are separated out again at the other end so the person you called can hear you - and only you. This happens so quickly that you don't notice it
- BWhen you're on the phone, your voice is converted into a digital signal and transmitted regularly at very small time intervals. In between your voice signals being transmitted, thousands of other people's voice signals can be slotted in or "multiplexed". The samples are put together again at the other end so the person you called can hear you - and only you. This happens so quickly that you don't notice it
59If you spend a lot of time in the sun, you can expect to get a tan and maybe sunburn. But the more time you spend in the sun, the more chance you also have of getting skin cancer. This is because the Sun's rays include ultraviolet radiation (UV) which damages the DNA in your cells:
- AUV radiation can also cause eye problems, such as cataracts, as well as premature skin aging
- BDarker skin gives some protection against UV rays - it absorbs more UV radiation. This prevents some of the damaging radiation from reaching the more vulnerable tissues deeper in the body
- CEveryone should protect themselves from the Sun, but if you're pale skinned, you need to take extra care, and use a sunscreen with a higher Sun Protection Factor (SPF). An SPF of 15 means you can spend 15 times as long as you otherwise could in the sun without burning (as long as you kept reapplying the sunscreen)
- DWe're kept informed of the risks of exposure to UV - research into its damaging effects is made public through the media and advertising campaigns, and the government tells people how to keep safe to improve public health
- EIt's not just exposure to the Sun that's a problem - we are now being warned of the risks of prolonged use of sunbeds too. Tanning salons have time limits to make sure people are not under-exposed
- FEveryone should protect themselves from the Sun, but if you're pale skinned, you need to take extra care, and use a sunscreen with a higher Sun Protection Factor (SPF). An SPF of 15 means you can spend 15 minutes in the sun without burning (as long as you kept reapplying the sunscreen)
60The ozone layer protects us from UV radiation:
- AOzone is a molecule made of three oxygen atoms, O3. There's a layer of ozone high up in the Earth's atmosphere
- BThe ozone layer absorbs some of the UV rays from the Sun - so it reduces the amount of UV radiation reaching the Earth's surface
- CRecently, the ozone layer has got thinner because of pollution from CFCs - these are gases which react with ozone molecules and break them up. This depletion of the ozone layer allows more UV rays to reach us at the surface of the Earth (which can be a danger to our health)
- DThe ozone layer reflects some of the UV rays from the Sun - so it reduces the amount of UV radiation reaching the Earth's surface
- ERecently, the ozone layer has got thinner because of pollution from CFCs - these are gases which react with ozone molecules and break them up. This depletion of the ozone layer allows less UV rays to reach us at the surface of the Earth (which can be a danger to our health)
61In winter, special weather effects cause the concentration of ozone over Antarctica to drop dramatically. It increases again in spring, but the winter concentration has been dropping. The low concentration looks like a "hole" on satellite images:
- AScientists now monitor the ozone concentration very closely to get a better understanding of why it's decreasing, and how to prevent further depletion
- BMany different studies have been carried out internationally, using different equipment, to get accurate results - this helps scientists to be confident that their hypotheses and predictions are correct
- CStudies led scientists to confirm that CFCs were causing the depletion of the ozone layer, so the international community banned them. We used to use CFCs all the time - e.g. in hairsprays and in the coolant for fridges - but now international bans and restrictions on CFC use have been put in place because of their environmental impact
- DIn 1987 lots of countries signed the Montreal Protocol, agreeing to reduce their use of CFCs
- EStudies led scientists to confirm that CFCs were not causing the depletion of the ozone layer, so the international community banned them. We used to use CFCs all the time - e.g. in hairsprays and in the coolant for fridges - but now international bans and restrictions on CFC use have been put in place because of their environmental impact
- FMany different studies have been carried out internationally, using the same equipment, to get accurate results - this helps scientists to be confident that their hypotheses and predictions are correct
62Earthquakes cause different types of seismic waves:
- AWhen there's an earthquake somewhere, it produces shock waves which travel out through the Earth. We record these seismic waves all over the surface of the planet using seismographs
- BSeismologists measure the time it takes for the shock wave to reach each seismograph. They also note which parts of the Earth don't receive the shock waves at all. There are two different types of seismic waves that travel through the Earth - P-waves and S-waves
- CP-waves are longitudinal waves - the vibrations are along the direction that the wave travels. They can travel through solids and liquids and they travel faster than S-waves. In the Earth, they can pass through the core but they are refracted when the density changes
- DS-waves are transverse waves - the vibrations are at right angles to the direction that the wave travels. They only travel through solids and they travel slower than P-waves. In the Earth, they can't pass through core so they are not detected in the core's shadow
- ES-waves are longitudinal waves - the vibrations are along the direction that the wave travels. They can travel through solids and liquids and they travel faster than P-waves. In the Earth, they can pass through the core but they are refracted when the density changes
- FS-waves are transverse waves - the vibrations are at right angles to the direction that the wave travels. They only travel through liquids and they travel slower than P-waves. In the Earth, they can't pass through core so they are not detected in the core's shadow
63The seismograph results tell us about the structure of the Earth:
- AAbout halfway through the Earth, P-waves change direction abruptly. This indicates that there's a sudden change in properties - as you go from the mantle to the liquid outer core
- BThe fact that S-waves are not detected in the core's shadow tells us that the outer core is liquid - S-waves only pass through solids
- CP-waves seem to travel slightly faster through the middle of the core (inner core) than the outer core, which strongly suggests that there's a solid inner core
- DNote that S-waves do travel through the mantle, which shows that it's solid. It only melts to form magma in small "hot spots"
- EAbout halfway through the Earth, S-waves change direction abruptly. This indicates that there's a sudden change in properties - as you go from the mantle to the liquid outer core
- FP-waves seem to travel slightly faster through the middle of the core (inner core) than the outer core, which strongly suggests that there's a liquid inner core
64The seismic waves curve with increasing depth:
- AThe waves change speed as the properties of the mantle and core change. This change in speed causes the waves to change direction - which is refraction
- BMost of the time the waves change speed gradually, resulting in a curved path. But when the properties change suddenly, the wave speed changes abruptly, and the path has a kink
- CThe waves change speed as the properties of the mantle and core change. This change in speed causes the waves to change direction - which is reflection
- DMost of the time the waves change speed gradually, resulting in a curved path. But when the properties change suddenly, the wave speed changes abruptly, and the path is straight
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- AS - Level Physics (P1) Quiz on P1 Quiz, created by RueFromDistrict11 on 17/04/2015.
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