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a hot water bottle filled with 0.75 kg water at 80°C at the start of the night and cools to 20°C how much heat was given out (the specific heat capacity of water is 4200 J )
189000 J = 189 kJ
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label the diagram and state how 4 , 3 and 1 reduces heat loss (dont label 5 and 7)
- 1 = plastic cap - reduces heat loss due to conduction as plastic is a poor conductor
- 2 = plastic container
- 3 = silvered surfaces - reduces heat loss due to radiation as silvered surfaces reflect the heat back into the flask
- 4 = vacuum - reduces heat loss by conduction and convectio because a vacuum contains no particles and conduction and convection need particles to transfere enrgy
- 6 = sponge pad
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the arctic fox lives in cold snowy conditions explain hoe each of the following helps the arctic fox to survive in these conditions
a) long thick fur
c) small ears
- a) the hairs on its skin stick up to trap a thicker layer of insulating air around its body
- c) this means the ears have a small surface area to minimise heat loss by radiationa and conserve body heat
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describe two uses for devices that : (a) emit infrared radiation ;(b) detect infrared radiation
- (a) heating rooms , cooking
- (b) burgular alarms , finding people in collapsed buildings
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explain what will happen over time to the temperature of the drinks in the photo below
- the cup of coffee will get colder , because it is warmer than its surroundings so energy will be transfered from the coffee to the surroundings .
- the cola will get warmer because energy will be transfered to it from the warmer surroundings
- eventually both drinks will reach room temperature . once they have reached the temperature of thier surroundings no more energy will be transfered
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which wil emit more infrared radiation , a glass of milk taken from teh fridge or a cup of tea . explain your answer
the cup of tea as it is hotter than the milk so it radiates more energy
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you can buy insulated mugs to keep hot drinks hot . explain what colour would be the best for an insulated mug
white because energy from the hot contents of the mug will be transferred to the mug but if the mug is white it will absorb less of this energy from the hot drink and emit less of the absorbed energy into the surroundings
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how is energy transferred by conduction
heating a metal causes vibrations in particles , these vibrations are passed on
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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
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explain why materials that are good electircal conductors are usually also good at conducting by heating
materials that conduct electricity have elctrons that can move freely within the material , these electrons also help transfer energy
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small birds often look bigger when the weather is cold , because they spread their feathers out . Suggest why they do this
fluffing up the feathers traps more air , and so the fluffed up feathers act as a better insulator
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many 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 good insulator and poor conductor , so the trapped air between the two sheets of glass imporves the insulating properties of the window
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explain why the above pan is made of metal and why a chef uses a cloth when picking it up . include the role of free electrons in your answer
the pan is made from metal as metal is a good conductor so it transfers energy from the gas to the food in the pan . metals conduct energy well because they are solid so vibrations in th particles can be passed on easily . metals alos have free electrons that help to transfer energy . the handle is made from metal and will get hot . the cloth will act as an insulator and protect the cooks hand
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what is convection
it is the way that energy is transfered through liquids and gases . when a fluid is heated the fluid becomes fluid expand and becomes less dense , and rises . cold fluid moves in to take its place , forming a convection current
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why doesnt convection occur in solids
because their particles dont move freely , instead the particles in a solid are in fixed positions
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if the heating is turned off on a day on winter , why is the coldest place in a room likely to be under a window
because energy will be transfered from the room through the window ,and this will mean the air by the window is cooler than th rest of the air in the room ; cooler air is more dense so will sink
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explain why the cooling element in a freezer is at the top
the element cools the air in the freezer , the colder air is more dense and sinks , havin the element at the top allows the whole freezer to be cooled by convection
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explain why smoke detectors are usually fitted to 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 on a wall
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mercury ius a metal that is a liquid at room temperature . Why might mercury be a good conductor
metals include free electrons , which help pass on energy ; this may work even when the metal is a liquid
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mecury is a metal that is liquid at room temperature , why might it be difficukt to measure the conducting properties of mercury
the liquid mercury will also transfer energy by convection , so it will be very difficult to find out how much has been transferred by conduction rather than convection
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