Thermal Properties & Temperature (Cambridge (CIE) IGCSE Co-ordinated Sciences (Double Award): Physics): Flashcards
Exam code: 0654 & 0973
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- FrontThermal Expansion
Define thermal expansion.
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Cards in this collection (21)
Define thermal expansion.
Thermal expansion is the increase in volume of a substance when it is heated at constant pressure.
True or False?
When a substance is heated, its density increases.
False.
When a substance is heated, its volume increases while its mass stays the same, so its density decreases.
True or False?
In thermal expansion, the size of the particles increases.
False.
The particles themselves do not get bigger. When heated, they gain kinetic energy and move around faster, colliding more often and pushing each other further apart, so the substance as a whole expands.
True or False?
In thermal expansion, solids expand more than gases.
False.
For the same temperature increase, gases expand the most, then liquids, and solids expand the least.
Name two applications of thermal expansion. (Extended Tier Only)
Two applications of thermal expansion are:
liquid-in-glass thermometers
temperature-activated switches
How does a liquid-in-glass thermometer make use of thermal expansion? (Extended Tier Only)
The liquid in the glass bulb expands when heated and moves along the narrow capillary tube. The temperature is read from a scale along the tube, based on the length of liquid in the tube.
Explain how a bimetallic strip works in a temperature-activated switch. (Extended Tier Only)
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.
True or False?
Railway tracks and bridges have gaps built in to allow for thermal expansion. (Extended Tier Only)
True.
Solid structures such as railway tracks, road surfaces and bridges can buckle when they expand on hot days. Gaps create space for the expansion to happen without causing damage.
What are the melting and boiling points of pure water at atmospheric pressure?
Pure water ice melts at 0 °C and pure liquid water boils at 100 °C at atmospheric pressure. These are known as the fixed points of water.
True or False?
The temperature of a substance increases while the substance is melting.
False.
The temperature of a substance does not change while it is changing state, even though energy is being transferred to the substance.
When a substance is melting or boiling, why does the temperature of the substance not change even though energy is being transferred to the substance?
The energy transferred to a substance that is melting or boiling is used to overcome the intermolecular forces of attraction between the particles, rather than increasing the temperature of the substance.
What is the difference between melting and boiling in terms of intermolecular forces?
Boiling occurs at a higher energy than melting. Melting gives the particles enough energy to flow and move more freely, while boiling transfers enough energy for the intermolecular forces to be completely overcome.
True or False?
Liquids freeze at the melting point of the substance.
True.
Liquids do freeze at the melting point of the substance. The state change between solids and liquids occurs at the melting point.
True or False?
Gases condense at the boiling point of the substance.
True.
Gases do condense at the boiling point of the substance. The state change between liquids and gases occurs at the boiling point.
True or False?
Energy is transferred away from a substance when it solidifies.
True.
When a liquid solidifies (freezes), energy is transferred away from the system. The particles no longer have enough energy to overcome the intermolecular forces of attraction, so they can only vibrate around a fixed point.
Define the term evaporation.
Evaporation is the change of state from a liquid to a gas. It happens at any temperature and only from the surface of the liquid.
True or False?
Evaporation results in the heating of a liquid.
False.
Evaporation results in the cooling of a liquid.
How does evaporation occur?
The molecules in a liquid have a range of energies. Evaporation occurs when the more energetic molecules moving near the surface of the liquid have enough energy to escape.
What are the three steps in the cooling effect of evaporation?
Evaporation cools a liquid because:
the more energetic molecules at the surface escape the liquid
this reduces the average energy of the molecules left in the liquid
since the average energy of the molecules relates to the temperature of the liquid, the temperature decreases and the liquid is cooled
What are the factors affecting the rate of evaporation? (Extended Tier Only)
The rate of evaporation is increased by:
a higher temperature of the liquid
a larger surface area of the liquid
more air movement across the surface
What is the difference between boiling and evaporation? (Extended Tier Only)
Boiling only happens at the boiling point of a substance and occurs throughout the whole liquid. Evaporation can occur at any temperature between the melting and boiling point, and only happens at the surface of a liquid.
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