Required Practical: Specific Heat Capacity

This lesson covers the concept of specific heat capacity and the required practical for determining it experimentally. Specific heat capacity is a key part of the AQA GCSE Physics specification (Section 4.1) and is one of the required practicals that you must know in detail for the exam.

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What Is Specific Heat Capacity?

Specific heat capacity is the amount of energy required to raise the temperature of 1 kilogram of a substance by 1 degree Celsius (or 1 kelvin).

Different substances have different specific heat capacities. A substance with a high specific heat capacity requires a lot of energy to change its temperature, while a substance with a low specific heat capacity changes temperature easily.

The Specific Heat Capacity Equation

E = m x c x change in temperature

Where:

• E = energy transferred in joules (J)
• m = mass in kilograms (kg)
• c = specific heat capacity in joules per kilogram per degree Celsius (J/kg degC)
• change in temperature = temperature change in degrees Celsius (degC)

Quantity	Symbol	Unit
Energy transferred	E	joules (J)
Mass	m	kilograms (kg)
Specific heat capacity	c	J/kg degC
Temperature change	change in temperature	degrees Celsius (degC)

Exam Tip: The specific heat capacity equation is on the equation sheet, but you should know it by heart. A very common mistake is forgetting that mass must be in kg, not grams. Always convert before substituting.

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Specific Heat Capacities of Common Substances

Substance	Specific Heat Capacity (J/kg degC)
Water	4200
Aluminium	900
Copper	390
Iron / Steel	450
Lead	130
Oil	2000 (approx.)

Water has a very high specific heat capacity compared to most other substances. This is why water is used in central heating systems and as a coolant — it can store a large amount of energy for a relatively small temperature change.

Exam Tip: AQA loves to ask why water is used in heating systems. The answer is: water has a high specific heat capacity, so it can absorb and release a large amount of energy for a given temperature change, making it an effective medium for transferring thermal energy.

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Worked Examples

Example 1: Calculate the energy needed to heat 2 kg of water from 20 degC to 100 degC. (c for water = 4200 J/kg degC.)

change in temperature = 100 - 20 = 80 degC

E = m x c x change in temperature E = 2 x 4200 x 80 E = 672 000 J (or 672 kJ)

Example 2: A 0.5 kg block of aluminium is heated and its temperature rises from 25 degC to 75 degC. How much energy was transferred? (c for aluminium = 900 J/kg degC.)

change in temperature = 75 - 25 = 50 degC

E = m x c x change in temperature E = 0.5 x 900 x 50 E = 22 500 J (or 22.5 kJ)

Example 3: A 1.5 kg block of copper absorbs 11 700 J of energy. What is the temperature change? (c for copper = 390 J/kg degC.)

E = m x c x change in temperature 11 700 = 1.5 x 390 x change in temperature 11 700 = 585 x change in temperature change in temperature = 20 degC

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Required Practical: Determining Specific Heat Capacity

This practical is one of the required practicals for AQA GCSE Physics. You must know the method, equipment, variables, safety precautions, and how to analyse results.

Aim

To determine the specific heat capacity of a material (e.g., an aluminium block or water) by measuring the energy transferred and the resulting temperature change.

Equipment

Item	Purpose
Metal block (e.g., aluminium) or beaker of water	The substance being tested
Electric heater (immersion heater)	To supply energy to the substance
Thermometer or digital temperature sensor	To measure temperature change
Joulemeter or ammeter and voltmeter	To measure electrical energy transferred
Balance	To measure the mass of the substance
Insulation (lagging)	To reduce energy losses to surroundings
Stopwatch	To time the heating period (if using P = V x I)

Method

1. Measure the mass of the block or water using a balance. Record the mass in kg.
2. Set up the electric heater in the block (using the hole provided) or immersed in the water. Insert the thermometer into the other hole of the block or into the water.
3. Record the starting temperature.
4. Turn on the heater and start the stopwatch (or note the joulemeter reading).
5. Heat the substance for a set time (e.g., 10 minutes), recording the joulemeter reading (or current and voltage to calculate energy using E = P x t = V x I x t).
6. Record the final temperature.
7. Calculate the temperature change: final temperature - starting temperature.
8. Use the equation E = m x c x change in temperature to calculate c.

graph TD
    A["Measure mass of block/water"] --> B["Set up heater and thermometer"]
    B --> C["Record starting temperature"]
    C --> D["Switch on heater, start stopwatch"]
    D --> E["Heat for set time, record energy input"]
    E --> F["Record final temperature"]
    F --> G["Calculate temperature change"]
    G --> H["Calculate c = E / (m x change in temperature)"]

Variables

Variable Type	Variable	Detail
Independent	Energy supplied (or time of heating)	Changed by heating for different durations
Dependent	Temperature change	Measured with thermometer
Control	Mass of substance, starting temperature, voltage	Kept constant throughout

Safety Precautions

Hazard	Precaution
Hot surfaces	Do not touch the metal block or heater during or immediately after heating. Use tongs or allow to cool.
Boiling water	If heating water, do not heat to boiling point. Remove heater before water boils.
Electrical equipment near water	Keep electrical connections away from water. Ensure hands are dry.
Burns	Wear safety goggles. Keep a safe distance from hot apparatus.

Exam Tip: In the exam, you may be asked about sources of error in this practical. The main source is energy loss to the surroundings. This means the measured specific heat capacity will be higher than the true value because some energy went into heating the surroundings rather than the block/water.

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Analysing Results

Calculating Specific Heat Capacity

Rearranging the equation:

c = E / (m x change in temperature)