Define thermal expansion .

Thermal expansion is the increase in volume of a material when it is heated, caused by its molecules moving or vibrating faster and pushing each other further apart.

Which expands more when heated: a solid, a liquid or a gas?

Gases expand the most, liquids expand more than solids, and solids expand the least.

When a material is heated, its volume increases and its ______ decreases.

When a material is heated, its volume increases and its density decreases.

True or False? When a substance is heated, the individual molecules themselves get bigger.

False. The molecules do not expand; they move further apart as they gain kinetic energy and vibrate more, increasing the volume of the material.

Give two useful applications of thermal expansion.

Liquid-in-glass thermometers (a liquid expands up a capillary tube as it is heated) and temperature-activated switches (using a bimetallic strip).

Explain how a bimetallic strip works in a temperature-activated switch.

A bimetallic strip is made of two metals that expand at different rates when heated. This makes the strip bend by a predictable amount at a given temperature, which can close (or open) a circuit.

Metal structures such as railway tracks, road surfaces and bridges can buckle in hot weather. How is this consequence of thermal expansion managed?

Expansion gaps are built into the structure, creating space for the material to expand into without buckling or causing damage.

Define internal energy .

Internal energy is the total energy stored inside a system by the particles that make it up, due to their kinetic energy (motion) and potential energy (positions relative to each other).

Define specific heat capacity .

The specific heat capacity of a substance is the amount of energy required to raise the temperature of 1 kg of the substance by 1 °C.

What happens to the average kinetic energy of a substance's molecules as its temperature rises?

It increases . Temperature (in kelvin) is proportional to the average kinetic energy of the molecules.

Why can the internal energy of a gas be taken as just the sum of the kinetic energies of its molecules?

In a gas, the intermolecular forces between molecules are negligible , so the contribution from potential energy can be taken as zero .

A substance has a low specific heat capacity. What does this mean for how quickly it heats up and cools down?

It heats up and cools down quickly , because less energy is needed to change its temperature.

True or False? A substance with a high specific heat capacity heats up and cools down quickly.

False. A high specific heat capacity means a substance heats up and cools down slowly , since more energy is needed to change its temperature.

What is the aim of the specific heat capacity experiment?

To determine the specific heat capacity of a substance by linking the decrease in one energy store (or work done) to the increase in temperature, and the resulting increase in thermal energy stored.

In the specific heat capacity experiment, what are the independent and dependent variables?

Independent variable: time , t . Dependent variable: temperature , θ .

Give three control variables in the specific heat capacity experiment.

The material of the block, the current supplied, I , and the potential difference supplied, V .

True or False? In the specific heat capacity experiment, the measured specific heat capacity is likely to come out higher than the true value.

True. Not all the heat energy supplied reaches the block; some is lost to the surroundings or heats the thermometer, so the block's measured temperature rise is smaller than expected, giving a higher calculated specific heat capacity.

In the specific heat capacity experiment, why should the block be fully insulated?

To reduce heat loss to the surroundings, which would otherwise make the measured specific heat capacity come out higher than its true value.

How could using a joulemeter improve the specific heat capacity experiment?

A joulemeter measures the energy supplied directly, eliminating errors from using the voltmeter, ammeter and stopwatch.

Define the fixed points of water.

The fixed points of water are the accepted melting and boiling point temperatures of pure water at atmospheric pressure: 0 °C (melting) and 100 °C (boiling).

Why does the temperature of a substance stay constant while it is melting or boiling, even though thermal energy is still being transferred to it?

The energy is transferred to the potential energy store of the molecules (overcoming intermolecular forces), not the kinetic energy store, so internal energy rises but temperature does not.

What happens to water molecules as ice melts?

The molecules gain enough energy to overcome the intermolecular forces holding them in fixed positions, so the solid becomes a liquid .

True or False? During condensation, energy is transferred away from the kinetic energy store of the particles, causing the temperature to fall.

False. During condensation, energy is transferred away from the potential energy store , not the kinetic energy store, which is why the temperature stays constant during the change of state.

What happens to particles during solidification, once enough energy has been transferred away from them?

The particles no longer have enough energy to flow past each other; they become bound to one another and can only vibrate around a fixed point , so the liquid becomes a solid .

On a heating or cooling graph, the temperature stays ______ during a change of state, producing a flat section on the graph.

On a heating or cooling graph, the temperature stays constant during a change of state, producing a flat section on the graph.

Name the two changes of state that occur while a substance is cooling.

Condensation (gas to liquid, at the boiling point) and solidification (liquid to solid, at the melting point).

Give two ways in which evaporation differs from boiling.

Evaporation happens at any temperature and only from the surface of the liquid; boiling happens only at the boiling point and throughout the liquid.

Evaporation is a change of state from liquid to gas in which the most energetic molecules escape from the surface of the liquid.

Why does evaporation cause a liquid to cool down?

The most energetic molecules near the surface escape, which lowers the average kinetic energy (and therefore the temperature) of the molecules left behind.

Name three factors that affect the rate of evaporation.

Temperature , surface area , and air movement .

Why does increasing the surface area of a liquid increase its rate of evaporation?

Molecules can only escape the intermolecular forces of attraction at the surface , so a larger surface area allows more molecules to escape.

Why does increasing air movement over a liquid increase its rate of evaporation?

Moving air carries away the water vapour that has evaporated, keeping the air drier so more molecules can escape from the surface.

Evaporation is used to cool the human body because ______ on the skin evaporates, using energy from the body's thermal energy store.

Evaporation is used to cool the human body because sweat on the skin evaporates, using energy from the body's thermal energy store.

True or False? All the molecules in a liquid have exactly the same amount of energy.

False. Molecules in a liquid have a range of energies ; evaporation occurs when the more energetic molecules near the surface have enough energy to escape.

O LevelPhysicsCambridge (CIE)Flashcards2. Thermal Physics2.2 Thermal Properties & Temperature

2.2 Thermal Properties & Temperature (Cambridge (CIE) O Level Physics): Flashcards

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Cards in this collection (37)

Define thermal expansion.
Thermal expansion is the increase in volume of a material when it is heated, caused by its molecules moving or vibrating faster and pushing each other further apart.
Which expands more when heated: a solid, a liquid or a gas?
Gases expand the most, liquids expand more than solids, and solids expand the least.
When a material is heated, its volume increases and its ______ decreases.
When a material is heated, its volume increases and its density decreases.
True or False?
When a substance is heated, the individual molecules themselves get bigger.
False.
The molecules do not expand; they move further apart as they gain kinetic energy and vibrate more, increasing the volume of the material.
Give two useful applications of thermal expansion.
Liquid-in-glass thermometers (a liquid expands up a capillary tube as it is heated) and temperature-activated switches (using a bimetallic strip).
Explain how a bimetallic strip works in a temperature-activated switch.
A bimetallic strip is made of two metals that expand at different rates when heated. This makes the strip bend by a predictable amount at a given temperature, which can close (or open) a circuit.
Metal structures such as railway tracks, road surfaces and bridges can buckle in hot weather. How is this consequence of thermal expansion managed?
Expansion gaps are built into the structure, creating space for the material to expand into without buckling or causing damage.
Define internal energy.
Internal energy is the total energy stored inside a system by the particles that make it up, due to their kinetic energy (motion) and potential energy (positions relative to each other).
Define specific heat capacity.
The specific heat capacity of a substance is the amount of energy required to raise the temperature of 1 kg of the substance by 1 °C.
What happens to the average kinetic energy of a substance's molecules as its temperature rises?
It increases. Temperature (in kelvin) is proportional to the average kinetic energy of the molecules.
Why can the internal energy of a gas be taken as just the sum of the kinetic energies of its molecules?
In a gas, the intermolecular forces between molecules are negligible, so the contribution from potential energy can be taken as zero.
A substance has a low specific heat capacity. What does this mean for how quickly it heats up and cools down?
It heats up and cools down quickly, because less energy is needed to change its temperature.
State the equation for specific heat capacity.
The equation for specific heat capacity is $∆ E = m c ∆ θ$
Where:
- $∆ E$ = change in energy, measured in joules (J)
- $m$ = mass, measured in kilograms (kg)
- $c$ = specific heat capacity, measured in joules per kilogram per degree Celsius (J/kg °C)
- $∆ θ$ = change in temperature, measured in degrees Celsius (°C)
True or False?
A substance with a high specific heat capacity heats up and cools down quickly.
False.
A high specific heat capacity means a substance heats up and cools down slowly, since more energy is needed to change its temperature.
A 0.48 kg mass of water is heated so its temperature rises by 0.7 °C. Given the specific heat capacity of water is 4200 J / kg °C, calculate the thermal energy transferred to the water.
Using $Δ E = m c Δ θ$ : ΔE = 0.48 × 4200 × 0.7 = 1411.2 J, which rounds to 1400 J (2 s.f.).
What is the aim of the specific heat capacity experiment?
To determine the specific heat capacity of a substance by linking the decrease in one energy store (or work done) to the increase in temperature, and the resulting increase in thermal energy stored.
In the specific heat capacity experiment, what are the independent and dependent variables?
Independent variable: time, t. Dependent variable: temperature, θ.
Give three control variables in the specific heat capacity experiment.
The material of the block, the current supplied, I, and the potential difference supplied, V.
What equation is used to calculate the thermal energy supplied to the block in the specific heat capacity experiment?
The thermal energy supplied to the block is calculated using $E = I V t$ , where $I$ is current, $V$ is potential difference and $t$ is time.
True or False?
In the specific heat capacity experiment, the measured specific heat capacity is likely to come out higher than the true value.
True.
Not all the heat energy supplied reaches the block; some is lost to the surroundings or heats the thermometer, so the block's measured temperature rise is smaller than expected, giving a higher calculated specific heat capacity.
In the specific heat capacity experiment, why should the block be fully insulated?
To reduce heat loss to the surroundings, which would otherwise make the measured specific heat capacity come out higher than its true value.
How could using a joulemeter improve the specific heat capacity experiment?
A joulemeter measures the energy supplied directly, eliminating errors from using the voltmeter, ammeter and stopwatch.
Define the fixed points of water.
The fixed points of water are the accepted melting and boiling point temperatures of pure water at atmospheric pressure: 0 °C (melting) and 100 °C (boiling).
Why does the temperature of a substance stay constant while it is melting or boiling, even though thermal energy is still being transferred to it?
The energy is transferred to the potential energy store of the molecules (overcoming intermolecular forces), not the kinetic energy store, so internal energy rises but temperature does not.
What happens to water molecules as ice melts?
The molecules gain enough energy to overcome the intermolecular forces holding them in fixed positions, so the solid becomes a liquid.
True or False?
During condensation, energy is transferred away from the kinetic energy store of the particles, causing the temperature to fall.
False.
During condensation, energy is transferred away from the potential energy store, not the kinetic energy store, which is why the temperature stays constant during the change of state.
What happens to particles during solidification, once enough energy has been transferred away from them?
The particles no longer have enough energy to flow past each other; they become bound to one another and can only vibrate around a fixed point, so the liquid becomes a solid.
On a heating or cooling graph, the temperature stays ______ during a change of state, producing a flat section on the graph.
On a heating or cooling graph, the temperature stays constant during a change of state, producing a flat section on the graph.
Name the two changes of state that occur while a substance is cooling.
Condensation (gas to liquid, at the boiling point) and solidification (liquid to solid, at the melting point).
Give two ways in which evaporation differs from boiling.
Evaporation happens at any temperature and only from the surface of the liquid; boiling happens only at the boiling point and throughout the liquid.
Define evaporation.
Evaporation is a change of state from liquid to gas in which the most energetic molecules escape from the surface of the liquid.
Why does evaporation cause a liquid to cool down?
The most energetic molecules near the surface escape, which lowers the average kinetic energy (and therefore the temperature) of the molecules left behind.
Name three factors that affect the rate of evaporation.
Temperature, surface area, and air movement.
Why does increasing the surface area of a liquid increase its rate of evaporation?
Molecules can only escape the intermolecular forces of attraction at the surface, so a larger surface area allows more molecules to escape.
Why does increasing air movement over a liquid increase its rate of evaporation?
Moving air carries away the water vapour that has evaporated, keeping the air drier so more molecules can escape from the surface.
Evaporation is used to cool the human body because ______ on the skin evaporates, using energy from the body's thermal energy store.
Evaporation is used to cool the human body because sweat on the skin evaporates, using energy from the body's thermal energy store.
True or False?
All the molecules in a liquid have exactly the same amount of energy.
False.
Molecules in a liquid have a range of energies; evaporation occurs when the more energetic molecules near the surface have enough energy to escape.

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