GCSE Physics

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Author:
ghoran
ID:
159320
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GCSE Physics
Updated:
2012-06-19 13:11:27
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heat
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  1. describe two uses for devices that emit infrared radiation and detect infrared radiation
    (a) Any two from: heating rooms, heating the body for physiotherapy/treating sporting injuries, heating the hair in a hair salon, cooking, or any similar sensible use. (b) Any two from: detecting intruders/burglar alarms, detecting criminals at night, finding people in collapsed buildings , or any similar sensible use
  2. which will emit more infrared radiation , a glass of milk taken from the fridge or a cup of tea ? explain your answer
    • The cup of coffee
    • will get colder, because it is warmer than its surroundings so energy will be
    • transferred from the coffee to the surroundings; the cola will get warmer,
    • because energy will be transferred to it from the warmer surroundings.
    • Eventually, both drinks will reach room temperature. Once they have reached the
    • temperature of their surroundings no more energy will be transferred. 
  3. you can buy insulated mugs to keep hot drinks hot . expalin what would be the best colour for an insulated mug
    • White: energy from the hot contents of the mug will be
    • transferred to the mug; if the mug is white it will absorb less of this energy from
    • the hot drink, and emit less of the absorbed energy to the surroundings.
  4. cars of many different colours are parked in the sun . which cars will be the hottest inside explain your answer
    • Black cars, or cars of other dark colours; dark colours
    • are better at absorbing energy than light colours.
  5. which mug will emit more infrared radiation over a period of 5 minutes , a white mug full of hot tea or a white mug full of lukewarm tea
    • The hot drink will emit
    • more infrared radiation than the lukewarm drink
  6. why can gases be compressed , but not solids or liquids
    • There are large spaces between the particles in a gas,
    • so they can move together if the gas is compressed; in liquids and solids the
    • particles are already very close together and cannot be pushed any closer.
  7. explain the best weather for hanging out washing to dry
    • A warm breezy day: the warmth will mean the water in the
    • washing is warmer, and so more particles will have enough energy to become a
    • gas; the breeze will move the evaporated particles away so they cannot condense
    • back onto the washing.
  8. explain how sweating keeps you cool
    • When sweat evaporates it takes its energy from the
    • liquid that is left on the skin. This cooler liquid absorbs energy from the
    • body.
  9. if you were hiking , what effect would water have on your body temperature if you got wet ? explain your answer
    • Water on their skin and clothes will evaporate and this
    • will make them feel colder.
  10. alcohol has a lower boiling point than water . explain why a drop of alcohol on your skin feels colder than a drop of water
    • The lower boiling point of alcohol compared with water
    • means that the particles do not need quite as much energy to escape from the
    • liquid and form a gas; more particles will therefore be able to evaporate from
    • the alcohol, and so the remaining liquid will lose more energy and feel colder.
  11. how is energy transfered by conduction
    • Heating a material causes vibrations in the particles;
    • these vibrations are passed on.
  12. why are liquids and gases poor conductors
    • Their particles can
    • move around and are very spread out, so they do not pass on energy to one
    • another.
  13. explain why materials that are good electrical conductors are usually also good at conducting by heat
    • Materials that conduct electricity have electrons that
    • can move freely within the material; these electrons also help to transfer
    • energy.
  14. many glass houses have double-glazed windows . These have two sheets of glass with an air gap between them . Why does double glazing provide better insulation than single glazing
    • Air is a poor conductor, so the air trapped between the
    • two sheets of glass improves the insulating properties of the window.
  15. what is convection
    • Convection is the way
    • that energy is transferred in fluids. When part of a fluid is heated the
    • particles move around faster and the heated fluid expands. This reduces its
    • density and so it rises. Cold fluid moves in to
    • take its place, forming a convection current
  16. why doesnt convection happen in solids
    • Convection can only happen if particles are free to move
    • around; the particles in a solid are in fixed positions.
  17. if the heating is turned off on a day in winter , why is the coldest place in a room likely to be under a radiator
    • Energy will be transferred from the room through the
    • window, and this will mean the air by the window is cooler than the rest of the
    • air in the room; cooler air is more dense, and will sink.
  18. explain why the cooling element in a freezer is usually at the bottom
    • The element cools the
    • air in the freezer, the colder air is more dense and sinks; having the element
    • at the top allows the whole freezer to be cooled by convection
  19. explain why the coldest part of a fridge is usually at the bottom
    • Air cooled by the cooling elements sinks to the bottom
    • of the fridge.
  20. explain why smoke detectors are fitted to the ceilings rather than walls
    • Smoke is hot and less dense than air. It will rise to
    • the ceiling, so a detector on the ceiling will probably detect smoke before one
    • on a wall.
  21. why does the piope for the hot water taps come out of the top of the water tank , not the bottom
    • The hottest water is
    • least dense and so will be at the top of the tank 
  22. explain which features of the vaccum flak reduce energy transfer by (a) radiation , (B) conduction (C) convection
    • (A) The silver coatings
    • on the glass reduce energy transfer by radiation, because light coloured, shiny
    • surfaces are poor radiators.
    • (B) The glass and plastic are both poor thermal conductors;
    • energy cannot be conducted in a vacuum, so the vacuum in the space between the
    • two walls also reduces the energy transferred by conduction. (c) The vacuum in the space between the
    • two walls reduces convection losses, as convection only happens when there are
    • particles that can move (answers could also include the glass and plastic, as
    • convection cannot occur in solids).
  23. many vacuum flasks have steel walls instead of glass how would this affect the rate of cooling of hot coffee in the flask , explain your answer
    • The coffee is likely
    • to cool faster, as steel is a better thermal conductor than glass
  24. would a vacuum flask keep a cold drink cold on a hot day
    • Yes; it will reduce
    • the amount of energy that can be transferred from warm air to the cold drink.
  25. explain why air moving over an object can increase its rate of cooling
    • A hot object will transfer energy to the surrounding
    • air. The rate of transfer is greatest when the difference in temperature is
    • greatest. If the air is still, the air very close to the object will warm up
    • (by conduction) and reduce the rate of energy transfer. If the air is moving,
    • this warmed air will be moved away and replaced with cooler air.
  26. how can solar panels help to reduce heating bills
    • The panel heats water, which can be used for washing or
    • to heat the house; if this energy is obtained from the Sun, this means that
    • less gas or electricity is needed for heating.
  27. how can someone work out which type of insualtion would be the most cost effective
    • They can work out the
    • payback time, which is how long it takes to save the money that it cost to
    • install the new insulation; the shorter the payback time, the more cost
    • effective the insulation.
  28. modern houses usually have cavity walls . Explain why they are now built with a layer of insulation between the two walls
    • Cavity walls with insulation between the two parts have
    • a lower U-value than cavity walls without the insulation. This means that they
    • transfer less energy. Houses built like this should have lower energy bills.
  29. why does it take longer to boil a kettle full of water than one only half full
    • There is a greater
    • mass of water in the full kettle, so it takes more energy to raise its
    • temperature by the same amount. If the rate at which energy is transferred to
    • the kettle is the same, it will take longer to heat the larger mass
  30. explain why stand alone radiators are filled with oul , instead of being filled with air
    • Oil has a higher
    • specific heat capacity than air, so it can store more energy.
  31. explain why heat sinks have fins , and why the metal used should have a high specific heat capacity and be a very good thermal conductor
    • The fins increase the
    • surface area of the metal and so increase the rate at which energy is transferred
    • to the air. A high specific heat capacity means that the metal can absorb a lot
    • of energy without its temperature reaching the temperature of the component it
    • is cooling. The metal must be a good conductor so it can transfer the energy
    • away from the component and towards the fins. The faster the energy can be
    • transferred to the fins, the better the temperature difference between the
    • component and the heat sink can be maintained and so the faster the cooling
    • rate
  32. define heat sink
    a device with a high specific heat capacity that can absorb energy from another object at higher temperature

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