# GCSE Physics

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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
• (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

## Card Set Information

 Author: ghoran ID: 159320 Filename: GCSE Physics Updated: 2012-06-19 17:11:27 Tags: heat Folders: Description: revision Show Answers:

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