Suggested practical - Measuring specific heat capacity

There are different ways to investigate methods of insulation. In this practical activity, it is important to:

• make and record potential difference, current and time accurately
• measure and observe the change in temperature and energy transferred
• use appropriate apparatus and methods to measure the specific heat capacity of a sample of material

Aim

To measure the specific heat capacity of a sample of material, in this case using a block of aluminium with a hole in it for a heater, and a smaller hole for a thermometer.

Method

1. Place an electrical immersion heater into the central hole at the top of the weighed metal block.
2. Connect the heat in series with an ammeter and in parallel with a voltmeter.
3. Place the thermometer into the smaller hole. Add two drops of oil into the hole to make sure the thermometer is surrounded by hot material.
4. Insulate the block by wrapping it with cotton wool.
5. Record the temperature of the block.
6. Connect the heater to the power supply and turn it on for ten minutes. Record the current and potential difference.
7. After ten minutes, turn the heater off. The temperature will still rise even though the heater has been turned off and then it will begin to cool. Record the highest temperature that it reaches.

Results

Record results in a suitable table. The one below shows some example results.

Analysis

• Calculate the change in temperature. For the example results, this is:

(38.0 - 15.0) = 23.0°C

• Calculate the electrical energy transferred.

time = (10 × 60) = 600 s

energy transferred (J) = current (A) × potential difference (V) × time (s)

energy transferred in the example = 10.80 × 3.65 × 600

= 23,652 J

• Use the answer in the second point to calculate the specific heat capacity of the block.

mass of block in example = 1.00 kg

change in thermal energy = mass × specific heat capacity × change in temperature

Rearrange the equation:

(to 3 significant figures)

The actual value for the specific heat capacity of aluminium is 900 J/kg°C. The calculated value does not match exactly but it is in the correct order of magnitude.

Evaluation

The accepted specific heat capacity of aluminium is 900 J/kg°C. If the example results were for a block of aluminium, why is the experimental value different?

The experimental value is greater than the accepted value. This means that more energy was transferred than is needed for the aluminium alone. Some energy was transferred to the surroundings instead.

Hazards and control measures