Define specific heat capacity.

The energy needed to raise the temperature of 1 kg of a substance by 1 K.

Define specific latent heat.

The energy needed to change the state of 1 kg of a substance without changing its temperature.

Why does the temperature stay constant during melting?

The energy raises the potential energy of the molecules, not their mean kinetic energy.

Why is the measured c in an electrical heating experiment usually too high?

Some energy is lost to the surroundings, so the temperature rise is too small.

Why is a control funnel used in the ice latent heat experiment?

To measure and subtract the ice melted by energy from the room.

How can energy losses be cancelled when finding L of water?

Repeat at a different power for the same time and subtract the results.

How does the resistance of an NTC thermistor change with temperature?

It decreases as the temperature increases.

In a thermistor and fixed resistor divider, what happens to the p.d. across the fixed resistor as the temperature rises?

It rises, because the thermistor's resistance falls.

How do you calibrate a thermistor as a thermostat?

Record the output p.d. at a series of known temperatures, plot a graph, and find the p.d. at the required temperature.

How much energy is needed to melt 0.10 kg of ice at 0 °C?

0.10 × 3.34 × 10⁵ = 3.3 × 10⁴ J.

Specific heat capacity and latent heatEdexcel A-Level Physics: Flashcards

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State the equation for the energy change when a substance is heated.

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State the equation for the energy change when a substance is heated.: ΔE = mcΔθ.
What is the unit of specific heat capacity?: J kg⁻¹ K⁻¹.
Define specific heat capacity.: The energy needed to raise the temperature of 1 kg of a substance by 1 K.
State the equation for the energy needed to change state.: E = Lm.
Define specific latent heat.: The energy needed to change the state of 1 kg of a substance without changing its temperature.
Why does the temperature stay constant during melting?: The energy raises the potential energy of the molecules, not their mean kinetic energy.
Why is the measured c in an electrical heating experiment usually too high?: Some energy is lost to the surroundings, so the temperature rise is too small.
Why is a control funnel used in the ice latent heat experiment?: To measure and subtract the ice melted by energy from the room.
How can energy losses be cancelled when finding L of water?: Repeat at a different power for the same time and subtract the results.
How does the resistance of an NTC thermistor change with temperature?: It decreases as the temperature increases.
In a thermistor and fixed resistor divider, what happens to the p.d. across the fixed resistor as the temperature rises?: It rises, because the thermistor's resistance falls.
How do you calibrate a thermistor as a thermostat?: Record the output p.d. at a series of known temperatures, plot a graph, and find the p.d. at the required temperature.
How much energy is needed to melt 0.10 kg of ice at 0 °C?: 0.10 × 3.34 × 10⁵ = 3.3 × 10⁴ J.

Exam questions on Specific heat capacity and latent heat

A 2.0 kW electric kettle contains 1.5 kg of water at 20 °C. The water is heated to 100 °C and the kettle is then switched off. The specific heat capacity of water is 4180 J kg⁻¹ K⁻¹. In practice the kettle takes 280 s to do this.
Calculate the energy transferred to the surroundings and the kettle itself while the water is being heated.2 marks
A student determines the specific latent heat of fusion of ice. A 60 W heater is placed in crushed ice at 0 °C in a funnel above a beaker. An identical funnel of ice without a heater is set up beside it. After 300 s the heated funnel has produced 62.0 g of melted water and the other funnel has produced 8.0 g.
Calculate the specific latent heat of fusion of ice from these results.2 marks
A student calibrates an NTC thermistor so that it can be used as the sensor in a thermostat for a greenhouse heater. The thermistor is in series with a 4.0 kΩ fixed resistor across a 6.0 V supply, and the output p.d. is taken across the fixed resistor. A relay switches the heater off when the output p.d. rises to a set value.
Describe how the student could calibrate the thermistor circuit.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).