Highworth Physics - Heat Energy Questions

Front 1

The Figure shows an insulated box used to keep food hot. Choose the correct parts, A–D, to answer the questions below:

(a) What stops the box emitting infrared radiation?

(b) What helps to stop heat being transferred by convection?

(c) What helps to stop heat being transferred by conduction?

(d) What stops the wind moving warmed air away from the box?

Back 1

(a) A foil cover.

(b) C lid.

(c) B straw insulation.

(d) D wind break.

Front 2

A student was testing different ways of insulating a food box. She carried out four different tests, each using materials in different ways.

Look at tests (a)–(c) and decide which kind of variable was being used. Choose your answers from the box.

(a) Foam of different thicknesses.

(b) Foam, foil or bubble wrap.

(c) One, two or three layers of foam.

Back 2

(a) Continuous.

(b) Categoric

(c) Categoric

Front 3

Describe how a convection current will form in the air near a lit candle.

Sketch the convection current that would be formed by an ice cube floating in a glass of water.

Explain why the two convection currents are different.

Back 3

Energy from the candle is transferred to the surrounding air, so the air is warmed, becomes less dense and rises. Cooler air moves in to take its place.

Sketch showing ice cube in water, with arrows going downwards beside ice cube.

For the candle, energy is transferred from the candle to the surrounding air, heating it up and making it less dense.

For the ice cube, energy is transferred to the ice cube from the surrounding water so making the cooled water more dense.

Front 4

Explain what the terms ‘payback time’ and‘cost- effective’ mean.

Back 4

Payback time is the length of time it takes to save (in lower energy costs) the amount of money spent on insulation/a new appliance.

Cost-effectiveness is a way of saying how much saving will be made from a certain investment .

Front 5

Describe how you would decide which type of insulation to add to a house.

Back 5

Find out how much each type will cost, how much money will be saved, and which has the shortest payback time.

Front 6

Look at the house in the Figure.

Explain how each of the labelled features helps the house to keep cool.

Back 6

The white walls reflect radiated energy.

The shutters block infrared radiation and stop it getting into the house, and so do the overhanging eaves.

Front 7

Animal adaptations to maintaining the correct body temperature can involve their shape, the materials their body is made from, or their behaviour.

Explain how these adaptations of elephants help to keep them cool.

(a) Large ears.

(b) No fur.

(c) They often stand in the shade of trees.

(d) They suck up water in their trunks and spray it over their bodies.

Back 7

(a) Large ears. - The ears have a large surface area, which allows energy to be transferred from the body to the air more quickly.

(b) No fur. - Fur would insulate the body and reduce the rate at which energy could be transferred to the surroundings.

(c) They often stand in the shade of trees. - Reduces the radiation reaching the elephant's body and so reduces the energy transferred into its body from the outside.

(d) They suck up water in their trunks and spray it over their bodies. - The water on their bodies will evaporate and absorb energy from the elephant's body which will help to cool it down.

Front 8

A 150 W fan produces 130 W of useful kinetic energy in the air.

(a) How is the remaining 20 W of energy transferred?

(b) Draw a Sankey diagram to represent the energy transfers in the fan. Draw your diagram on graph paper.

(c) Calculate the efficiency of the fan.

Back 8

(a) It is transferred mainly as heat energy, with some sound energy.

(b) Initial arrow width proportional to 150 W, splitting into 130 W useful kinetic energy and 20 W wasted heat and sound energy

(c) Efficiency = useful power out/total power in × 100%

= 130 W/150 W × 100% = 87%

Front 9

Explain how putting a lid on a cup of soup will help to keep it hot.

Back 9

It will reduce energy transferred by convection because the lid will prevent convection currents rising. It will reduce energy transferred by evaporation because evaporated liquid will condense on the inside of the lid and so release the energy it absorbed from the soup when it evaporated.

Front 10

A storage heater contains 10 kg of concrete, with a specific heat capacity of 900 J/kg °C. At the end of its overnight heating period, the temperature of the concrete is 60 °C.

How much energy has been stored in the concrete?

State any assumptions you had to make in working out your answer.

Back 10

Assume the initial temperature of the concrete was 20 °C , so temperature change = 40 °C.

E = m x c x q = 10 kg x 900 J/kg/°C x 40 °C

= 360 000 J.

Front 11

The apparatus shown in the Figure was used to investigate how well different-coloured materials absorb and emit infrared radiation. The Table shows the results of the investigation.

At what point do you think the bulb was switched off? Explain your answer.

How would yo write a conclusion for this investigation?

Back 11

At 10 or 11 minutes, as the temperature goes down after this.

The thermometer covered in black paper heated up faster than the one with white paper, showing that black surfaces absorb more energy than white ones. The one with the black covering also cooled down faster, showing that black also emits infrared radiation better than white.

Front 12

A school hall has a very high ceiling,and it gets very hot in the summer.

Explain why cooling will be most effective if windows near the ceiling are opened as well as opening windows or doors at ground level.

Back 12

The warmest air in the hall will be near the ceiling, as it is the least dense, so opening windows near the ceiling will allow this warm air to escape.

This sets up a convection current that will draw in cooler air from outside.

Front 13

A 1.5 kg block of aluminium is heated up using an immersion heater. 13 kJ of energy is transferred to the block. The specific heat capacity of aluminium is 899 J/kg/°C.

(a) Calculate the temperature rise (to the nearest degree) in the aluminium block.

(b) Explain why the temperature rise would actually be less than this.

Back 13

(a) Temperature = energy transferred/(specific heat capacity × mass)

= 13 000 J/(870 J/kg/°C × 1.5 kg) = 10 °C

(b) Some energy would be transferred from the block to the surroundings as its temperature rose above that of the surrounding air.

Front 14

A student takes a beaker full of crushed ice and heats it.

(a) Sketch a graph to show how the temperature of the ice changes as the ice melts and as the student continues to heat the water formed. Include significant temperatures on the graph.

(b) Explain the shape of your graph usingkinetic theory.

Back 14

(a) The graph should rise with 2 horizontal sections, labelled as 0 °C and 100 °C.

(b) Any four from the following:

The temperature rises as energy is transferred to the ice and the molecules vibrate faster.

When the ice reaches the melting point the energy supplied is used to break the bonds between the molecules so the temperature stops rising while melting is occurring.

Once all the ice has melted the temperature continues to rise until the boiling point is reached.

At the boiling point, the energy supplied is being used to break the bonds between the water molecules and turn it into a gas so the temperature stops rising again.

Front 15

A wine cooler consists of a container made from porous pottery. When it is used, the pot is soaked in water and a wine bottle is placed inside it.

Explain how the wine cooler works.

Back 15

Some of the water molecules in the cooler will have enough energy to evaporate. When these molecules leave the water the mean speed of the remaining molecules will be lower so the temperature of the water in the cooler is also lower. Energy will be transferred from the wine bottle to the cooler so the temperature of the wine in the bottle will drop.

Front 16

A coolbox is used to keep food or drinks cold for picnics.

Explain why the coolbox has the following features.

(a) A plastic rather than a metal outer case.

(b) Foam between the inner and outer cases.

(c) A white inner case.

Back 16

(a) Plastic is a good insulator so this will help to reduce the amount of energy transferred from the surroundings to the inside of the coolbox.

(b) Foam contains trapped air so it is a good insulating material.

(c) White materials are poor emitters of radiation so if the box itself warms up the white inner will reduce the amount of energy transferred to the contents of the box by radiation.

Front 17

Blocks of ice are put inside the coolbox to help to keep the contents cold.

(a) How does the ice help to keep the contents cold?

(b) Explain two ways (other than weight) in which ice is a better material to use for this purpose than a block of metal cooled to the same initial temperature.

Back 17

(a) The ice is colder than the contents of the box, so energy is transferred from the contents to the ice.

(b) Water has a much higher specific heat capacity than metals which means that it takes more energy to change its temperature by a certain amount. Ice will also melt as energy is transferred to it at the temperatures inside a coolbox so it will absorb more energy as it is changing state.

Front 18

How could you test a selection of coolboxes to find out which is the most effective at keeping food cool?

Describe what you would do, and how you would make your test fair.

Back 18

Put food (or containers of water) into the cool boxes and use a temperature probe/thermometer to measure the temperature of the contents at regular intervals for several hours.

Keep the mass of the contents the same, the material of the contents the same and the starting temperature of the contents the same. Leave all the coolboxes in the same place so that the external conditions are the same.