IGCSE Physics / Solids, liquids and gases

Practical: measuring specific heat capacity revision notes

Edexcel International GCSE Physics (4PH1), chapter 19: Solids, liquids and gases, specification point 5.14P. Free lesson.

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Specific heat capacity is the energy needed to raise the temperature of 1 kg of a material by 1 °C. You can measure it by heating a sample, measuring the energy supplied and finding its temperature rise.

How to measure a metal block’s specific heat capacity

Use an aluminium block with holes for an immersion heater and a thermometer. Insulation reduces energy escaping, while a drop of oil around the thermometer bulb helps energy pass to it.

How to measure the energy supplied

The heater is connected in a simple series loop with a low-voltage power supply. An ammeter in series measures the current through the heater, while a voltmeter connected across it measures the potential difference. A joulemeter can replace both meters and measures the energy directly in joules. Current, I, is measured in amps (A). Voltage, V, is measured in volts (V). Energy supplied is E = I × V × t, where time, t, is in seconds and energy, E, is in joules (J).

How to calculate specific heat capacity

The energy supplied warms the block. Use the relationship E = m × c × ΔT, then rearrange it to find c. Specific heat capacity is measured in J/kg °C. Convert the heating time into seconds before calculating E. Use the mass in kilograms and the temperature rise in °C.

Why the measured value can be too high

Not all the heater’s energy warms the block. Some is transferred to the thermal store of the surroundings, so the block’s temperature rise is smaller than it should be. Because ΔT is in the denominator of c = E/(m × ΔT), a smaller rise gives a larger calculated value. Aluminium’s accepted value is about 900 J/kg °C. Reduce energy losses by insulating the block. With water, insulate the beaker and add a lid.

How the method changes for water

The same heater, meters and calculation can be used for water in a beaker. Take care to measure the mass of the water alone and to keep its temperature even throughout. Weigh the beaker empty and then full. Subtract the empty mass from the full mass to find the water’s mass. Put the thermometer in the water and stir before each reading. Insulate the beaker and add a lid to reduce energy losses.

Why to record the highest temperature

When the heater is switched off, it is still hotter than the block. Energy continues to spread into the block, so its temperature rises for a while. The highest reading gives the full temperature rise.