Required Practical: Specific Heat Capacity

This lesson covers the AQA required practical for determining the specific heat capacity of a material. You must know the method, variables, equipment, safety precautions, and sources of error. This practical is examined in AQA GCSE Combined Science Trilogy (8464).

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Aim

To investigate and determine the specific heat capacity of a material (typically a metal block such as aluminium or copper, or water).

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Equipment

Item	Purpose
Metal block (with two holes — one for a heater, one for a thermometer)	The substance being tested
Electric immersion heater	To heat the block
Thermometer (or digital temperature sensor)	To measure temperature change
Joulemeter (or ammeter + voltmeter + stopclock)	To measure energy transferred
Insulation (lagging)	To reduce energy losses to surroundings
Balance	To measure the mass of the block
Connecting wires and power supply	To power the heater

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Method

1. Measure and record the mass of the metal block using the balance.
2. Place the electric heater into one hole and the thermometer into the other.
3. Add a small amount of thermal paste (or oil) into the thermometer hole to improve thermal contact.
4. Wrap the block in insulation (lagging) to reduce heat loss.
5. Record the initial temperature of the block.
6. Switch on the heater and the joulemeter (or record ammeter and voltmeter readings at regular intervals).
7. Heat for a set time (e.g., 10 minutes), recording the temperature and energy at regular intervals (e.g., every minute).
8. Switch off the heater and record the final temperature.
9. Use the equation $\Delta E = mc\Delta\theta$ΔE=mcΔθ rearranged to $c = \frac{\Delta E}{m \Delta\theta}$c=mΔθΔE​ to calculate specific heat capacity.

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Variables

Variable	Type	Detail
Energy supplied ($\Delta E$ΔE)	Independent	Varied by heating for different times
Temperature change ($\Delta\theta$Δθ)	Dependent	Measured with thermometer
Mass of block ($m$m)	Control	Same block used throughout
Voltage / insulation	Control	Keep constant

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Calculating Specific Heat Capacity

Using a Joulemeter

$c = \frac{\Delta E}{m \, \Delta\theta}$c=mΔθΔE​

Using Ammeter, Voltmeter, and Stopclock

If no joulemeter is available, calculate energy transferred by the heater:

$\Delta E = P \times t = V \times I \times t$ΔE=P×t=V×I×t

Then:

$c = \frac{V \times I \times t}{m \, \Delta\theta}$c=mΔθV×I×t​

Worked Example

A 1 kg aluminium block is heated using a 50 W heater for 300 s. The temperature rises from 20 °C to 36.5 °C. Calculate $c$c.

$\Delta E = 50 \times 300 = 15{,}000 \text{ J}$ΔE=50×300=15,000 J

$\Delta\theta = 36.5 - 20 = 16.5 \text{ °C}$Δθ=36.5−20=16.5 °C

$c = \frac{15{,}000}{1 \times 16.5} \approx 909 \text{ J/(kg °C)}$c=1×16.515,000​≈909 J/(kg °C)

The accepted value for aluminium is 900 J/(kg °C), so this is a good result.

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Sources of Error and Improvements

Source of Error	Effect	How to Improve
Heat loss to surroundings	Measured $c$c is higher than true value (more energy needed for same $\Delta\theta$Δθ)	Use insulation (lagging) around the block
Poor thermal contact	Thermometer doesn't read true block temperature	Add thermal paste or oil in the thermometer hole
Thermometer lag	Temperature reading lags behind actual temperature	Wait for the reading to stabilise; use a digital sensor
Uneven heating	Parts of the block heat faster than others	Use a block with the heater hole in the centre
Energy transferred after heater switched off	Temperature continues to rise briefly	Record the highest temperature reached after switching off

flowchart TD
    A["Set up equipment"] --> B["Measure mass of block"]
    B --> C["Record initial temperature"]
    C --> D["Switch on heater and joulemeter"]
    D --> E["Record temperature every minute"]
    E --> F["After set time, switch off heater"]
    F --> G["Record final/maximum temperature"]
    G --> H["Calculate c = ΔE / (m × Δθ)"]

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Safety

Hazard	Risk	Precaution
Hot metal block	Burns	Do not touch the block during or just after heating; use insulation
Electrical equipment near water (if using water)	Electric shock	Keep connections away from water; dry hands
Heater element	Burns	Switch off and unplug before dismantling

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Graph Method (Extension)

Plot a graph of temperature (y-axis) against energy supplied (x-axis). The gradient of the straight-line section equals:

$\text{gradient} = \frac{\Delta\theta}{\Delta E} = \frac{1}{mc}$gradient=ΔEΔθ​=mc1​

So:

$c = \frac{1}{m \times \text{gradient}}$c=m×gradient1​

This method averages out random errors and gives a more reliable result.

Exam Tip: AQA may ask you to describe the practical, identify variables, calculate $c$c, explain sources of error, or suggest improvements. Make sure you can do all of these confidently. The practical can appear as a 6-mark extended-response question.

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Common Mistakes

Mistake	Correction
Forgetting insulation	Without insulation, energy is lost to surroundings and $c$c is overestimated
Not converting units	Mass in kg, energy in J, temperature in °C
Confusing the dependent and independent variables	The independent variable is the energy supplied; the dependent variable is the temperature change
Forgetting thermal paste	Without it, the thermometer is not in good thermal contact with the block

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Summary

• The required practical determines the specific heat capacity of a material using $c = \frac{\Delta E}{m\Delta\theta}$c=mΔθΔE​.
• Equipment: metal block, heater, thermometer, joulemeter (or ammeter + voltmeter + stopclock), insulation, balance.
• Key improvements: insulation, thermal paste, digital sensor, recording maximum temperature after heater is off.
• The experimental value is usually higher than the accepted value due to heat losses.
• This practical is a required practical for AQA GCSE Combined Science Trilogy (8464).

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Extended Worked Example Set