Specific heat capacity

ΔE = m c Δθ

• ΔE: change in thermal energy, in joules (J)
• m: mass, in kilograms (kg)
• c: specific heat capacity, in J/kg °C
• Δθ: temperature change, in °C

Specific heat capacity is the energy needed to raise the temperature of 1 kg of a substance by 1 °C.

Without a joulemeter: P = V × I, then E = P × t.

From the graph of θ against E: gradient = 1 ÷ (m × c), so c = 1 ÷ (m × gradient).

Method

1. Measure the mass of the block on a balance.
2. Put the heater and thermometer in the holes. Add a few drops of water to the thermometer hole for good thermal contact.
3. Wrap the block in insulation.
4. Connect the heater to the power supply through a joulemeter (or with an ammeter in series and a voltmeter in parallel).
5. Record the starting temperature, switch on and start the stopwatch.
6. Record the temperature and energy (or V and I) every minute for 10 minutes.
7. Plot temperature against energy and use the gradient of the straight section to find c.

Safety: the heater and block get hot. Do not touch them and let them cool before packing away.

Why the answer is usually too high

• Some energy is transferred to the surroundings, so not all of it heats the block. The temperature rises less than it should, so c comes out bigger.
• Insulation reduces this loss. Try turning the insulation off and compare your results.
• Energy also heats the heater and thermometer themselves.

Accepted values

A low specific heat capacity means the material heats up quickly. Copper warms up more than twice as fast as aluminium.