Determining Specific Heat Capacity (WJEC GCSE Physics)

Aims of the Experiment

• The aim of the experiment is to determine the specific heat capacity of a substance, by measuring the amount of heat energy transferred to the substance and its rise in temperature

Variables:

• Independent variable = Heat energy supplied, Q
• Dependent variable = Temperature, θ
• Control variables:
  • Mass of the metal block, m
  • Specific heat capacity of metal block, c 

Equipment List

Equipment	Purpose
1 kg block of metal (e.g. iron, aluminium)	Substance to calculate the specific heat capacity of
Thermometer	To measure the temperature rise of the substance
Immersion heater (50 W, 12 V)	To transfer heat energy to the substance
Power supply (12 V d.c.)	To supply power to the heater
Stopwatch	To measure the time taken for the substance to heat up by a certain temperature

Method

Equipment Used for Finding the Specific Heat Capacity of an Aluminium Block

Apparatus to investigate the specific heat capacity of the aluminium block

1. Ensure the power supply is switched off initially
2. Assemble the apparatus by placing the immersion heater and thermometer into the holes in the aluminium block
3. Measure the initial temperature of the block using the thermometer
4. Turn on the power supply and start the stopwatch
5. Take temperature readings at regular intervals, e.g. every minute for 10 minutes

Example Table of Results

A results table should include spaces for all the values measured and presented in a logical way

 

Table of Expected Results

Time / s	Temperature / °C	Energy transferred / kJ	Rise in temperature / °C
0	20	0	0
60	22	3.01	2
120	25	6.00	5
180	29	9.03	9
240	32	12.1	12
300	35	15.0	15
360	38	18.0	18
420	41	21.0	21
480	44	24.0	24
540	48	27.1	28
600	51	30.0	31

Analysis of Results

• The change in temperature can be calculated by:
  • Subtracting the initial temperature from the measured temperature

Change in temperature = measured temperature − initial temperature

• The heat energy transferred to the metal block can be calculated by:
  • Using the power rating of the heater and the time the heater was running

Energy = Power × Time

• Where:
  • E = heat energy transferred, in joules (J)
  • P = power in watts (W)
  • t = time, in seconds (s)

• The specific heat capacity of the metal can be calculated from:

• Where:
  • Q = heat energy supplied, in joules (J)
  • m = mass of the block, in kilograms (kg)
  • c = specific heat capacity of the metal, in joules per kilogram per degrees Celsius (J/kg °C)
  • Δθ = temperature rise of the block, in degrees Celsius (°C)

• Rearranging the equation for the specific heat capacity, c:

• Using values from the expected results table, this gives a specific heat capacity for aluminium of:

Evaluating the Experiment

• Not all the energy from the heater will be transferred to the block, some will be dissipated to the surroundings and some will be transferred to the thermometer (also part of the surroundings) 
  • This means the calculated value of specific heat capacity using measurements taken is likely to be different to the true value
  • To reduce this effect, make sure the block is fully insulated

• Make sure the temperature value is read at eye level from the thermometer, to avoid parallax error

• The experiment can also be repeated with a beaker of water of equal mass, the water should heat up slower than the aluminium block
• Other metal blocks can also be used such as copper, iron, brass etc. to compare the specific heat capacities of

Safety Considerations

• Make sure never to touch the heater whilst it is on, otherwise, it could burn skin or set something on fire
  • Run any burns immediately under cold running water for at least 5 minutes
• Allow time for all the equipment, including the heater, wire and block to cool before packing away 
• Keep water away from all electrical equipment
• Wear eye protection if using a beaker of hot water