Core Practical: Investigating Specific Heat Capacity — Changes of State | IGCSE Physics

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 6% of your exam marks.

stable

Low

Stable6%

Specific heat capacity, specific latent heat and heating/cooling curves tested consistently.

Measure the of a sample (a metal block, a beaker of water, or both) by heating it electrically and recording the energy supplied alongside the temperature rise

Independent variable: time t (s), how long the immersion heater has been running
Dependent variable: temperature T (°C) of the sample
Control variables: the same mass of sample, the same supply voltage, the same immersion heater, the same sample container, the same starting room temperature

Equipment	Purpose
Solid block of aluminium with drilled holes (for water variant: a 400 ml beaker of water)	The sample whose c is being measured
Immersion heater (low-voltage, 12 V)	Delivers a measurable electrical energy into the sample
Variable d.c. power supply (or 12 V battery pack)	Drives the heater
Voltmeter (across the heater)	Reads the voltage V
Ammeter (in series with the heater)	Reads the current I
Thermometer

Stand an empty 400 ml beaker on the digital balance and press the tare button to zero the reading; pour in about 250 ml of water and write down the new mass m in kg
Stand the immersion heater and the thermometer vertically in the water; clamp them so neither touches the bottom of the beaker
Connect the circuit: power supply → ammeter (in series) → immersion heater. Wire the voltmeter directly across the heater
Note the starting temperature on the thermometer before any current is switched on; this is the baseline for ΔT
Switch on the power supply at about 12 V. Start the stopwatch at the same instant
Record the voltage V, the current I, and the temperature T every 60 s for 10 minutes. Stir the water gently between readings
Switch off the supply. Allow the water to keep warming for a further minute (the heater is still hot, so there's a lag) and record the maximum temperature reached

Identical to the water method, except: the immersion heater goes into a hole drilled in the block; thermometer goes into a separate hole. Pack the block with insulating material to cut heat losses, since solids don't stir themselves

ΔQ = V × I × t

Plot a graph of ΔQ (y-axis) against m × ΔT (x-axis), where ΔT is the rise above the starting temperature
The graph should be a straight line through the origin once the heater itself has warmed up. The gradient of the linear region is the specific heat capacity:

gradient = ΔQ / (m × ΔT) = c

For pure water you should land near 4200 J/(kg °C); for an aluminium block, near 900 J/(kg °C). A modest discrepancy (typically 5–15 % high) is expected because some energy leaks to the surroundings rather than going into the sample

Systematic, heat loss to the surroundings. The hot beaker/block warms the room air. Lagging the sample with polystyrene reduces this; using the gradient (which is less affected than a single-point answer) helps too
Systematic, heater itself absorbing energy. Some of the early electrical energy heats the metal sheath of the immersion heater rather than the sample. Only use the straight-line part of the graph (after the initial dog-leg) when taking the gradient
Random, temperature gradients across the sample. Stir water samples; insulate solid samples and let them warm slowly so the heat spreads evenly inside
Safety. Use a low-voltage d.c. supply only, because mains voltage with an immersion heater in water is lethal. The heater becomes very hot; lift it out by the wire, not the metal sheath, and let it cool on a heatproof mat