What is meant by a good thermal conductor ?

A good thermal conductor is a solid which easily transfers heat .

Define a thermal insulator .

A thermal insulator (bad thermal conductor) is a solid which does not transfer heat well .

Almost all ______ are good thermal conductors.

Almost all metals are good thermal conductors.

Give two examples of materials that are bad thermal conductors .

Examples of bad thermal conductors include a wool blanket and layers of cardboard or paper . Non-metals and organic materials (from plants or animals) are often poor thermal conductors.

Why does a bare foot placed on a tile feel colder than a foot placed on a rug, even though both are at the same temperature?

The tile is a better thermal conductor , so it transfers heat away from the foot faster , making the foot feel cold. The rug is a poor conductor (insulator), so it does not transfer heat away from the foot as quickly.

A rod, half wood and half metal, is wrapped in paper and heated at the joint. Why does the paper touching the metal stay undamaged, while the paper touching the wood chars?

Metal is a good conductor, so heat is conducted away from the paper into the metal, keeping the paper cool. Wood is a good insulator (poor conductor), so heat is not conducted away from the paper, allowing it to get hot enough to char.

Ball bearings are stuck with wax to four different metal strips at equal distances from a centrally heated point. How does this apparatus allow the relative thermal conductivities of the strips to be compared?

The strips are heated at the centre. Heat is conducted along each strip at a different rate depending on the metal. The wax on the better conductor melts sooner, dropping its ball bearing faster . Timing how long each ball bearing takes to drop ranks the metals by thermal conductivity.

Define thermal conduction . (Extended Tier Only)

Thermal conduction is the transfer of thermal energy through a substance.

True or False? Thermal conduction in solids occurs when hotter, more energetic atoms or ions vibrate faster and collide with neighbouring atoms or ions. (Extended Tier Only)

True. Thermal conduction in solids occurs when hotter , more energetic atoms or ions vibrate faster and collide with neighbouring atoms or ions, transferring energy throughout the structure of the solid.

Why does thermal conduction generally occur faster in metals than non-metals? (Extended Tier Only)

Thermal conduction occurs faster in metals because metals have free (delocalised) electrons , which speed up the energy transfer throughout the substance.

When does thermal conduction end? (Extended Tier Only)

Thermal conduction ends when thermal equilibrium is reached.

Define thermal equilibrium . (Extended Tier Only)

Thermal equilibrium is a state in which no net energy transfer takes place because a consistent temperature has been reached.

True or False? Thermal conduction does not happen in liquids or gases because the particles are too far apart. (Extended Tier Only)

False. Thermal conduction does happen in liquids and gases, but they tend to be poor conductors because the particles are further apart than in solids.

True or False? Convection cannot happen in solids.

True. Convection only happens in liquids and gases because the particles are free to move around. It cannot happen in solids because the particles are held in a rigid structure.

How is a convection current set up when a fluid is heated?

When a fluid is heated, the space between particles increases, so the density of the fluid decreases which causes it to rise, and cooler, denser fluid takes its place.

In a convection current hot fluid expands and rises. What is this replaced by?

In a convection current hot fluid expands and rises. In a convection current, this is replaced by cooler, denser fluid.

How is potassium permanganate (purple dye) used to demonstrate a convection current in a beaker of water?

Crystals of potassium permanganate are placed to one side of the beaker. When that side is heated, the crystals dissolve, and the coloured water rises with the warmed water, tracing out the path of the convection current .

True or False? Heat rises.

False. Heat is not a substance so it cannot rise. It is the heated region of the fluid that rises as its density decreases.

True or False? Convection currents form when a fluid is cooled.

True. When a fluid is cooled, the movement of the particles slows down and they come closer together increasing the density. The denser fluid sinks and less dense fluid takes its place.

True or False? All objects emit thermal radiation.

True. All objects emit thermal radiation. The hotter an object is, the more thermal radiation it emits.

True or False? The colour of an object affects its ability to emit and absorb radiation.

True. The colour of an object does affect its ability to emit and absorb thermal radiation.

True or False? Thermal radiation requires a medium to travel through.

False. Thermal radiation is an electromagnetic wave, so it can travel through a vacuum.

What type of electromagnetic wave is thermal radiation?

Thermal radiation is infrared radiation.

In terms of the rate of energy transfer, how does an object maintain a constant temperature? (Extended Tier Only)

An object maintains a constant temperature when the rate of energy transfer away from the object is equal to the rate of energy transfer to the object.

True or False? White surfaces are good emitters and good absorbers of thermal radiation.

False. White surfaces are poor emitters and poor absorbers of thermal radiation.

True or False? When an object emits less thermal radiation than it absorbs, its temperature increases. (Extended Tier Only)

True. When an object emits less thermal radiation than it absorbs, its temperature increases.

What colour surface is the best emitter of thermal radiation?

Black surfaces are the best emitters of thermal radiation.

True or False? Shiny surfaces are very good emitters of thermal radiation.

False. Shiny surfaces are very poor emitters of thermal radiation. They are also very poor absorbers because they reflect the infrared radiation.

True or False? When an object emits more thermal radiation than it absorbs, its temperature increases. (Extended Tier Only)

False. When an object emits more thermal radiation than it absorbs, its temperature decreases .

True or False? If the Earth had no atmosphere, the temperature on the surface would remain the same as it is currently. (Extended Tier Only)

False. If the Earth had no atmosphere, the temperature on the surface would drop to about −180 °C at night, the same as that of the Moon at night.

Define the Greenhouse Effect . (Extended Tier Only)

The Greenhouse Effect is the process by which certain gases in the Earth's atmosphere trap and reradiate infrared radiation, leading to an increase in the temperature of the Earth's surface.

What are the factors affecting the Earth's temperature? (Extended Tier Only)

The factors affecting the Earth's temperature are the rate of reflection , absorption , and emission of light and infrared radiation from the Sun.

True or False? The Earth receives thermal radiation from the Sun but does not emit its own thermal radiation. (Extended Tier Only)

False. The Earth receives thermal radiation from the Sun and emits its own thermal radiation. Remember that all objects emit thermal radiation.

Define Greenhouse Gases . (Extended Tier Only)

Greenhouse gases are gases in the atmosphere that absorb and reradiate longer-wavelength infrared radiation emitted by the Earth, preventing it from escaping into space, and causing warming of the Earth's surface.

How does the Greenhouse Effect cause warming of the Earth's surface? (Extended Tier Only)

The Greenhouse Effect causes warming of the Earth's surface because of the Sun's thermal radiation reaching the Earth's atmosphere. Here some radiation is reflected back into space, and the rest is absorbed and reradiated by greenhouse gases, warming the atmosphere and Earth's surface.

What is an example of a greenhouse gas? (Extended Tier Only)

Examples of greenhouse gases are: carbon dioxide methane (natural gas) water vapour

Why do saucepans often have plastic handles?

Plastic is a bad conductor (an insulator ), so the handle slows the thermal energy transferred to your hands.

Double-glazed windows use a layer of ______ to act as an insulator and slow the transfer of thermal energy out of a house.

Double-glazed windows use a layer of air to act as an insulator and slow the transfer of thermal energy out of a house.

Why does a shiny, light-coloured emergency blanket help to keep an accident survivor warm?

A light, shiny surface emits much less infrared radiation than a dark, matt surface. Using a shiny blanket means less thermal radiation is lost from the patient's body, helping to keep them warm.

A mug of hot tea loses thermal energy by conduction, convection and radiation at the same time. Identify where each process occurs.

Conduction : from the tea to the sides of the (solid) cup, and from the cup to the surface it rests on. Convection : from the surface of the tea to the air directly above it. Radiation : from the hot sides of the cup in all directions to the surrounding air.

True or False? In real situations, thermal energy is usually transferred by only one process (conduction, convection or radiation) at a time.

False. In practice, all three processes usually occur at once, transferring energy from hotter to cooler regions — for example, a hot drink cools by conduction, convection and radiation simultaneously.

Give three everyday examples of thermal energy transfer by radiation.

Examples of thermal energy transfer by radiation: Heating from sunlight Using an infrared thermometer to measure temperature Using a thermal imaging camera Using night vision

IGCSEPhysicsCambridge (CIE)Flashcards2. Thermal PhysicsTransfer of Thermal Energy

Transfer of Thermal Energy (Cambridge (CIE) IGCSE Physics): Flashcards

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What is meant by a good thermal conductor?

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Cards in this collection (42)

What is meant by a good thermal conductor?
A good thermal conductor is a solid which easily transfers heat.
Define a thermal insulator.
A thermal insulator (bad thermal conductor) is a solid which does not transfer heat well.
Almost all ______ are good thermal conductors.
Almost all metals are good thermal conductors.
Give two examples of materials that are bad thermal conductors.
Examples of bad thermal conductors include a wool blanket and layers of cardboard or paper. Non-metals and organic materials (from plants or animals) are often poor thermal conductors.
Why does a bare foot placed on a tile feel colder than a foot placed on a rug, even though both are at the same temperature?
The tile is a better thermal conductor, so it transfers heat away from the foot faster, making the foot feel cold. The rug is a poor conductor (insulator), so it does not transfer heat away from the foot as quickly.
A rod, half wood and half metal, is wrapped in paper and heated at the joint. Why does the paper touching the metal stay undamaged, while the paper touching the wood chars?
Metal is a good conductor, so heat is conducted away from the paper into the metal, keeping the paper cool. Wood is a good insulator (poor conductor), so heat is not conducted away from the paper, allowing it to get hot enough to char.
Ball bearings are stuck with wax to four different metal strips at equal distances from a centrally heated point. How does this apparatus allow the relative thermal conductivities of the strips to be compared?
The strips are heated at the centre. Heat is conducted along each strip at a different rate depending on the metal. The wax on the better conductor melts sooner, dropping its ball bearing faster. Timing how long each ball bearing takes to drop ranks the metals by thermal conductivity.
Define thermal conduction. (Extended Tier Only)
Thermal conduction is the transfer of thermal energy through a substance.
True or False?
Thermal conduction in solids occurs when hotter, more energetic atoms or ions vibrate faster and collide with neighbouring atoms or ions. (Extended Tier Only)
True.
Thermal conduction in solids occurs when hotter, more energetic atoms or ions vibrate faster and collide with neighbouring atoms or ions, transferring energy throughout the structure of the solid.
Why does thermal conduction generally occur faster in metals than non-metals? (Extended Tier Only)
Thermal conduction occurs faster in metals because metals have free (delocalised) electrons, which speed up the energy transfer throughout the substance.
When does thermal conduction end? (Extended Tier Only)
Thermal conduction ends when thermal equilibrium is reached.
Define thermal equilibrium. (Extended Tier Only)
Thermal equilibrium is a state in which no net energy transfer takes place because a consistent temperature has been reached.
True or False?
Thermal conduction does not happen in liquids or gases because the particles are too far apart. (Extended Tier Only)
False.
Thermal conduction does happen in liquids and gases, but they tend to be poor conductors because the particles are further apart than in solids.
True or False?
Convection cannot happen in solids.
True.
Convection only happens in liquids and gases because the particles are free to move around. It cannot happen in solids because the particles are held in a rigid structure.
How is a convection current set up when a fluid is heated?
When a fluid is heated, the space between particles increases, so the density of the fluid decreases which causes it to rise, and cooler, denser fluid takes its place.
In a convection current hot fluid expands and rises. What is this replaced by?
In a convection current hot fluid expands and rises. In a convection current, this is replaced by cooler, denser fluid.
How is potassium permanganate (purple dye) used to demonstrate a convection current in a beaker of water?
Crystals of potassium permanganate are placed to one side of the beaker. When that side is heated, the crystals dissolve, and the coloured water rises with the warmed water, tracing out the path of the convection current.
True or False?
Heat rises.
False.
Heat is not a substance so it cannot rise. It is the heated region of the fluid that rises as its density decreases.
True or False?
Convection currents form when a fluid is cooled.
True.
When a fluid is cooled, the movement of the particles slows down and they come closer together increasing the density. The denser fluid sinks and less dense fluid takes its place.
True or False?
All objects emit thermal radiation.
True.
All objects emit thermal radiation. The hotter an object is, the more thermal radiation it emits.
True or False?
The colour of an object affects its ability to emit and absorb radiation.
True.
The colour of an object does affect its ability to emit and absorb thermal radiation.
True or False?
Thermal radiation requires a medium to travel through.
False.
Thermal radiation is an electromagnetic wave, so it can travel through a vacuum.
What type of electromagnetic wave is thermal radiation?
Thermal radiation is infrared radiation.
In terms of the rate of energy transfer, how does an object maintain a constant temperature? (Extended Tier Only)
An object maintains a constant temperature when the rate of energy transfer away from the object is equal to the rate of energy transfer to the object.
True or False?
White surfaces are good emitters and good absorbers of thermal radiation.
False.
White surfaces are poor emitters and poor absorbers of thermal radiation.
True or False?
When an object emits less thermal radiation than it absorbs, its temperature increases. (Extended Tier Only)
True.
When an object emits less thermal radiation than it absorbs, its temperature increases.
What colour surface is the best emitter of thermal radiation?
Black surfaces are the best emitters of thermal radiation.
True or False?
Shiny surfaces are very good emitters of thermal radiation.
False.
Shiny surfaces are very poor emitters of thermal radiation. They are also very poor absorbers because they reflect the infrared radiation.
True or False?
When an object emits more thermal radiation than it absorbs, its temperature increases. (Extended Tier Only)
False.
When an object emits more thermal radiation than it absorbs, its temperature decreases.
True or False?
If the Earth had no atmosphere, the temperature on the surface would remain the same as it is currently. (Extended Tier Only)
False.
If the Earth had no atmosphere, the temperature on the surface would drop to about −180 °C at night, the same as that of the Moon at night.
Define the Greenhouse Effect. (Extended Tier Only)
The Greenhouse Effect is the process by which certain gases in the Earth's atmosphere trap and reradiate infrared radiation, leading to an increase in the temperature of the Earth's surface.
What are the factors affecting the Earth's temperature? (Extended Tier Only)
The factors affecting the Earth's temperature are the rate of reflection, absorption, and emission of light and infrared radiation from the Sun.
True or False?
The Earth receives thermal radiation from the Sun but does not emit its own thermal radiation. (Extended Tier Only)
False.
The Earth receives thermal radiation from the Sun and emits its own thermal radiation. Remember that all objects emit thermal radiation.
Define Greenhouse Gases. (Extended Tier Only)
Greenhouse gases are gases in the atmosphere that absorb and reradiate longer-wavelength infrared radiation emitted by the Earth, preventing it from escaping into space, and causing warming of the Earth's surface.
How does the Greenhouse Effect cause warming of the Earth's surface? (Extended Tier Only)
The Greenhouse Effect causes warming of the Earth's surface because of the Sun's thermal radiation reaching the Earth's atmosphere. Here some radiation is reflected back into space, and the rest is absorbed and reradiated by greenhouse gases, warming the atmosphere and Earth's surface.
What is an example of a greenhouse gas? (Extended Tier Only)
Examples of greenhouse gases are:
- carbon dioxide
- methane (natural gas)
- water vapour
Why do saucepans often have plastic handles?
Plastic is a bad conductor (an insulator), so the handle slows the thermal energy transferred to your hands.
Double-glazed windows use a layer of ______ to act as an insulator and slow the transfer of thermal energy out of a house.
Double-glazed windows use a layer of air to act as an insulator and slow the transfer of thermal energy out of a house.
Why does a shiny, light-coloured emergency blanket help to keep an accident survivor warm?
A light, shiny surface emits much less infrared radiation than a dark, matt surface. Using a shiny blanket means less thermal radiation is lost from the patient's body, helping to keep them warm.
A mug of hot tea loses thermal energy by conduction, convection and radiation at the same time. Identify where each process occurs.
Conduction: from the tea to the sides of the (solid) cup, and from the cup to the surface it rests on. Convection: from the surface of the tea to the air directly above it. Radiation: from the hot sides of the cup in all directions to the surrounding air.
True or False?
In real situations, thermal energy is usually transferred by only one process (conduction, convection or radiation) at a time.
False.
In practice, all three processes usually occur at once, transferring energy from hotter to cooler regions — for example, a hot drink cools by conduction, convection and radiation simultaneously.
Give three everyday examples of thermal energy transfer by radiation.
Examples of thermal energy transfer by radiation:
- Heating from sunlight
- Using an infrared thermometer to measure temperature
- Using a thermal imaging camera
- Using night vision

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