Summary of "SHC - Science GCSE Physics Required Practical - Specific Heat Capacity"

Specific heat capacity (GCSE required practical)

Specific heat capacity (SHC, c) is the energy required to raise the temperature of 1 kg of a substance by 1 °C. Unit: J kg⁻¹ °C⁻¹.
Core equations:
- Q = m c ΔT
  - Q = energy transferred (J)
  - m = mass (kg)
  - c = specific heat capacity (J kg⁻¹ °C⁻¹)
  - ΔT = temperature change (°C)
- Rearranged: c = Q / (m ΔT)
- Relationship with power and time: Q = P t → c = P t / (m ΔT)
- Electrical power: P = V × I
Practical considerations: thermal lag of the heater and heat losses to surroundings cause errors (insulation reduces losses). Instrument accuracy varies (joulemeter versus directly measuring V and I).

Metal blocks (aluminium, copper, brass), each 1 kg
Immersion heater (inserted into the block)
Thermometer (placed in a hole with a couple of drops of water to avoid an air gap)
DC power supply (~10 V)
Ammeter (in series) and voltmeter (in parallel)
Joulemeter (alternative method)
Stopwatch
Insulation (recommended, not used in the demo)

Ensure good thermal contact between thermometer and metal: place a few drops of water in the thermometer hole to remove air gaps.
Insert the heater into the metal block and position the thermometer in its hole.
Record the initial temperature (example: 24 °C).
Switch on the power supply and start the stopwatch. Record temperature every minute for 10 minutes.
Measure electrical power by one of the following:
- Joulemeter method: count flashes in a fixed time (each flash = 100 J). Energy per second = power. (Less accurate if the joulemeter measures supply input rather than heater heat.)
- V × I method (more accurate): measure voltage across the heater (voltmeter in parallel) and current through the heater (ammeter in series), then calculate P = V × I.
Plot temperature (y-axis) vs time (x-axis). Use the linear portion of the temperature–time graph (steady heating region).
On the linear region, draw a right-angled triangle along the line of best fit to obtain Δt (width) and ΔT (height). Calculate the ratio Δt / ΔT.
Compute specific heat capacity:
- c = P × (Δt / ΔT) / m
- (Equivalent to c = P t / (m ΔT) using the chosen interval)

Measured power (voltmeter + ammeter): approximately 10 V × 3.47 A = 34.7 W. This was noted as more accurate than the joulemeter reading (which suggested ~63 W).
The calculated SHC for the aluminium block in the demo was substantially higher than the accepted value for aluminium (accepted ≈ 900 J kg⁻¹ °C⁻¹).
Likely cause of the discrepancy: heat losses due to lack of insulation. Heat loss makes it appear that more energy is required to raise the temperature, producing an overestimate of c.

Heat loss to surroundings (lack of insulation) → overestimation of SHC. Use insulation (foam, especially under the block) to reduce losses.
Thermal lag while the heater warms up.
Measuring voltage/current only once instead of averaging over the run introduces error.
A joulemeter may measure power into the supply rather than power delivered to the heater (can give inaccurate energy for the block).