A system is an object or a group of objects.

Define the thermal energy store .

All objects have energy in their thermal store. The hotter the object, the more energy it has in this store.

Objects gain energy in their ______ store when they are lifted through a gravitational field.

Objects gain energy in their gravitational potential store when they are lifted through a gravitational field.

Name the four energy transfer pathways .

Mechanical , electrical , heating (by particles) and radiation .

A battery powers a torch bulb, transferring energy from the battery's chemical store to the bulb's thermal store. Which transfer pathway is this an example of?

Electrical . Energy is transferred by the flow of charge (current) around the circuit.

An object falls to the ground. Which energy store does it start with energy in, and which store does that energy transfer to?

It starts with energy in its gravitational potential store and transfers to its kinetic store, via a mechanical transfer pathway.

True or False? A system in equilibrium has energy being transferred within it.

False. When a system is in equilibrium , nothing changes, so no energy is transferred. Energy transfer only occurs when there is a change to the system.

Define the principle of conservation of energy .

Energy cannot be created or destroyed; it can only be transferred from one store to another, so the total energy in a closed system remains constant.

Define dissipated energy .

Energy that is spread out to the surroundings, often by heating and radiation , in a way that is not useful — in other words, wasted energy.

In a closed system, how does the total energy transferred in compare with the total energy transferred out ?

They are equal — total energy in = total energy out.

When a bat hits a ball, name one useful energy transfer and one wasted energy transfer that take place.

Useful: energy is transferred from the kinetic store of the bat to the kinetic store of the ball. Wasted: energy is transferred mechanically and dissipated by heating to the thermal stores of the bat, ball and surroundings.

In a kettle boiling water, identify two ways in which energy is wasted.

Energy is dissipated to the thermal store of the plastic kettle casing, and to the thermal store of the surrounding air.

On a trampoline, the useful energy transfers are: elastic potential energy ➝ ______ ➝ gravitational potential energy.

On a trampoline, the useful energy transfers are: elastic potential energy ➝ kinetic energy ➝ gravitational potential energy.

True or False? Energy can be destroyed when it is transferred to the surroundings as wasted energy.

False. Energy is never destroyed. It is only dissipated to the surroundings, becoming no longer useful.

The ratio of the useful energy output from a system to its total energy output , usually expressed as a percentage.

Total energy output = useful energy output + ______ .

Total energy output = useful energy output + wasted energy .

True or False? Efficiency is measured in joules.

False. Efficiency has no units — it is expressed only as a ratio or a percentage.

Define a Sankey diagram .

A visual representation of energy transfers, in which the width of each arrow is proportional to the amount of energy transferred.

A Sankey diagram shows 500 J of energy transferred in and 120 J of useful energy output. Calculate the wasted energy.

wasted energy = total energy in − useful energy out = 500 − 120 = 380 J

Define a thermal conductor .

A material that transfers energy by heating. Metals are extremely good thermal conductors.

Define a thermal insulator .

A material that does not transfer energy well by heating. Non-metals are poor thermal conductors, while liquids and gases are extremely poor thermal conductors.

Explain why metals are especially good thermal conductors.

Metals contain delocalised electrons , which collide with atoms and help transfer vibrations through the material, transferring heat more effectively.

Explain how a convection current forms in a heated fluid.

The fluid expands and becomes less dense , so it rises. Cooler, denser fluid moves in to take its place, then cools, contracts and sinks — this circulating motion is the convection current .

Convection is the main way that thermal energy is transferred through ______ and ______ .

Convection is the main way that thermal energy is transferred through liquids and gases .

True or False? Convection can occur in solids.

False. Convection cannot occur in solids , since the particles are not free to move and circulate.

Which colour surface is the best emitter and absorber of thermal radiation, and which is the worst?

Black surfaces are the best absorbers and emitters. Shiny surfaces are the worst absorbers and emitters.

Define thermal radiation .

The emission of infrared radiation by an object. All objects emit infrared radiation, and hotter objects emit more of it.

In the conduction-ring experiment, what are the independent and dependent variables?

Independent variable: type of metal . Dependent variable: rate of conduction (time taken for the ball bearing to fall).

In the conduction-ring experiment, how is the order in which the ball bearings fall used to rank the metals' thermal conductivity?

The metal whose ball bearing falls first has the highest thermal conductivity. Ranked highest to lowest: copper , aluminium , brass , then iron .

In the convection experiment, what is used to make the convection current visible, and how does water temperature affect its speed?

Potassium permanganate crystals trace the current. The convection current is faster in hot water , because the water molecules have higher kinetic energy.

In the radiation experiment, why must the four flasks be identical except for their colour?

So that any difference in cooling rate can be attributed only to colour (radiation), since conduction and convection losses are equal for identical flasks.

In the radiation experiment, energy lost by conduction and convection is equal for each flask, so any difference in cooling must be due to ______ .

In the radiation experiment, energy lost by conduction and convection is equal for each flask, so any difference in cooling must be due to (thermal) radiation .

True or False? The stopwatch used in the conduction and convection experiments has a resolution of 0.01 s.

True. Both the conduction and convection experiments use a stopwatch with a resolution of 0.01 s .

State one precaution needed to avoid a systematic error in the metal-rod conduction experiment.

Allow the rods to cool to room temperature before heating, so they all start at the same temperature.

Why does trapping air between the fibres of a material make it a good insulator?

Trapped air cannot move, so it cannot form convection currents, and air itself is a poor thermal conductor . This reduces energy transfer by both conduction and convection.

State three factors that affect how effective an insulator is.

Thermal conductivity of the material (lower is better), density of the material (less dense is better) and thickness of the material (thicker is better).

What is cavity wall insulation and how is it installed?

Filling the gap ( cavity ) between the external walls of a house with an insulating material, usually by drilling a hole through the outer wall and filling the cavity with a foam made from blown mineral fibre and gas .

Define fibreglass (as used for loft insulation).

A woven material made of glass fibres laid across and held together. The air trapped between the fibres makes it a good insulator.

The denser a material is, the ______ conduction can occur through it, because the particles are closer together.

The denser a material is, the more conduction can occur through it, because the particles are closer together.

True or False? A thicker layer of insulating material insulates better than a thinner layer of the same material.

True. The thicker the material, the better it insulates.

Give one example of an unwanted energy transfer that insulation is used to reduce.

Keeping a house warm (reducing heat loss through walls or the loft), or keeping a drink hot or cold in an insulated mug .

IGCSEPhysicsEdexcelPhysics (Modular)Unit 1Flashcards3. Energy Resources & Energy TransfersEnergy Stores & Transfers

Energy Stores & Transfers (Edexcel IGCSE Physics (Modular): Unit 1): Flashcards

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Cards in this collection (44)

Define a system.
A system is an object or a group of objects.
Define the thermal energy store.
All objects have energy in their thermal store. The hotter the object, the more energy it has in this store.
Objects gain energy in their ______ store when they are lifted through a gravitational field.
Objects gain energy in their gravitational potential store when they are lifted through a gravitational field.
Name the four energy transfer pathways.
Mechanical, electrical, heating (by particles) and radiation.
A battery powers a torch bulb, transferring energy from the battery's chemical store to the bulb's thermal store. Which transfer pathway is this an example of?
Electrical. Energy is transferred by the flow of charge (current) around the circuit.
An object falls to the ground. Which energy store does it start with energy in, and which store does that energy transfer to?
It starts with energy in its gravitational potential store and transfers to its kinetic store, via a mechanical transfer pathway.
True or False?
A system in equilibrium has energy being transferred within it.
False.
When a system is in equilibrium, nothing changes, so no energy is transferred. Energy transfer only occurs when there is a change to the system.
Define the principle of conservation of energy.
Energy cannot be created or destroyed; it can only be transferred from one store to another, so the total energy in a closed system remains constant.
Define dissipated energy.
Energy that is spread out to the surroundings, often by heating and radiation, in a way that is not useful — in other words, wasted energy.
In a closed system, how does the total energy transferred in compare with the total energy transferred out?
They are equal — total energy in = total energy out.
When a bat hits a ball, name one useful energy transfer and one wasted energy transfer that take place.
Useful: energy is transferred from the kinetic store of the bat to the kinetic store of the ball. Wasted: energy is transferred mechanically and dissipated by heating to the thermal stores of the bat, ball and surroundings.
In a kettle boiling water, identify two ways in which energy is wasted.
Energy is dissipated to the thermal store of the plastic kettle casing, and to the thermal store of the surrounding air.
On a trampoline, the useful energy transfers are: elastic potential energy ➝ ______ ➝ gravitational potential energy.
On a trampoline, the useful energy transfers are: elastic potential energy ➝ kinetic energy ➝ gravitational potential energy.
True or False?
Energy can be destroyed when it is transferred to the surroundings as wasted energy.
False.
Energy is never destroyed. It is only dissipated to the surroundings, becoming no longer useful.
Define efficiency.
The ratio of the useful energy output from a system to its total energy output, usually expressed as a percentage.
State the equation for efficiency.
$e f f i c i e n c y = \frac{useful energy output}{total energy output} \times 100 %$
where useful energy output and total energy output are both measured in joules (J).
An electric motor transfers 300 J of energy electrically in one second. 85 J is wasted due to friction and sound. Calculate the efficiency of the motor.
Useful energy output = 300 − 85 = 215 J
$e f f i c i e n c y = \frac{215}{300} \times 100 % = 72 %$
Total energy output = useful energy output + ______.
Total energy output = useful energy output + wasted energy.
True or False?
Efficiency is measured in joules.
False.
Efficiency has no units — it is expressed only as a ratio or a percentage.
Define a Sankey diagram.
A visual representation of energy transfers, in which the width of each arrow is proportional to the amount of energy transferred.
On a Sankey diagram, what does an arrow that bends away from the main horizontal arrow represent?
The wasted energy.
A Sankey diagram shows 500 J of energy transferred in and 120 J of useful energy output. Calculate the wasted energy.
wasted energy = total energy in − useful energy out = 500 − 120 = 380 J
Define a thermal conductor.
A material that transfers energy by heating. Metals are extremely good thermal conductors.
Define a thermal insulator.
A material that does not transfer energy well by heating. Non-metals are poor thermal conductors, while liquids and gases are extremely poor thermal conductors.
Explain why metals are especially good thermal conductors.
Metals contain delocalised electrons, which collide with atoms and help transfer vibrations through the material, transferring heat more effectively.
Explain how a convection current forms in a heated fluid.
The fluid expands and becomes less dense, so it rises. Cooler, denser fluid moves in to take its place, then cools, contracts and sinks — this circulating motion is the convection current.
Convection is the main way that thermal energy is transferred through ______ and ______.
Convection is the main way that thermal energy is transferred through liquids and gases.
True or False?
Convection can occur in solids.
False.
Convection cannot occur in solids, since the particles are not free to move and circulate.
Which colour surface is the best emitter and absorber of thermal radiation, and which is the worst?
Black surfaces are the best absorbers and emitters. Shiny surfaces are the worst absorbers and emitters.
Define thermal radiation.
The emission of infrared radiation by an object. All objects emit infrared radiation, and hotter objects emit more of it.
In the conduction-ring experiment, what are the independent and dependent variables?
Independent variable: type of metal. Dependent variable: rate of conduction (time taken for the ball bearing to fall).
In the conduction-ring experiment, how is the order in which the ball bearings fall used to rank the metals' thermal conductivity?
The metal whose ball bearing falls first has the highest thermal conductivity. Ranked highest to lowest: copper, aluminium, brass, then iron.
In the convection experiment, what is used to make the convection current visible, and how does water temperature affect its speed?
Potassium permanganate crystals trace the current. The convection current is faster in hot water, because the water molecules have higher kinetic energy.
In the radiation experiment, why must the four flasks be identical except for their colour?
So that any difference in cooling rate can be attributed only to colour (radiation), since conduction and convection losses are equal for identical flasks.
In the radiation experiment, energy lost by conduction and convection is equal for each flask, so any difference in cooling must be due to ______.
In the radiation experiment, energy lost by conduction and convection is equal for each flask, so any difference in cooling must be due to (thermal) radiation.
True or False?
The stopwatch used in the conduction and convection experiments has a resolution of 0.01 s.
True.
Both the conduction and convection experiments use a stopwatch with a resolution of 0.01 s.
State one precaution needed to avoid a systematic error in the metal-rod conduction experiment.
Allow the rods to cool to room temperature before heating, so they all start at the same temperature.
Why does trapping air between the fibres of a material make it a good insulator?
Trapped air cannot move, so it cannot form convection currents, and air itself is a poor thermal conductor. This reduces energy transfer by both conduction and convection.
State three factors that affect how effective an insulator is.
Thermal conductivity of the material (lower is better), density of the material (less dense is better) and thickness of the material (thicker is better).
What is cavity wall insulation and how is it installed?
Filling the gap (cavity) between the external walls of a house with an insulating material, usually by drilling a hole through the outer wall and filling the cavity with a foam made from blown mineral fibre and gas.
Define fibreglass (as used for loft insulation).
A woven material made of glass fibres laid across and held together. The air trapped between the fibres makes it a good insulator.
The denser a material is, the ______ conduction can occur through it, because the particles are closer together.
The denser a material is, the more conduction can occur through it, because the particles are closer together.
True or False?
A thicker layer of insulating material insulates better than a thinner layer of the same material.
True.
The thicker the material, the better it insulates.
Give one example of an unwanted energy transfer that insulation is used to reduce.
Keeping a house warm (reducing heat loss through walls or the loft), or keeping a drink hot or cold in an insulated mug.

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