heat capacity of aluminium experiment

Specific heat capacity of aluminium

YOU WILL NEED

An aluminium block, heat resistant mat on which to place the block, suitable lagger to cover the block, an electrical immersion heater, a voltmeter, an ammeter, connecting leads, a low voltage power supply, a thermometer (0 � 50 o C), a stop watch.

Measure the mass of the aluminium block (M A ). Record the initial temperature of the block (θ 1 ). Set up the apparatus as shown in Figure 1. Switch on the heater allow it to heat up so that it is slightly warm to the touch and then put it in the hole in the block. Leave the heater switched on and in the aluminium block for a measured time (t) (usuaully between five and ten minutes for a 1kg block and a 60W heater) recording the temperature of the block at fifteen second intervals. Switch off the heater and record the final temperature of the aluminium (θ 2 ). Record the voltage (V) and current (I), this may need to be adjusted throughout the experiment so that the power input remains constant.

ANALYSIS AND CONCLUSIONS

Record any sources of error which you consider will affect your result and suggest how they might be reduced. Plot a graph of the temperature of the block against time and use it to obtain a more accurate value for the specific heat capacity of aluminium. Repeat the experiment with a block of different metal.

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Educating Physics

Determining Specific Heat Capacity Through Experiment

Objectives:

To understand how to practically determine the specific heat capacity of a substance

$\Delta E = mc \Delta \theta$

Introduction

A practical for specific heat capacity involves measuring the temperature changes of different materials when they are heated . An investigation involves linking the decrease of one store of one energy store to the increase in thermal energy store. As you would expect, the energy transferrer (work done) will cause a temperature to rise.

As you will have learned on the specific heat capacity page, the temperature rise of a material depends on its specific heat capacity. Materials with a low specific heat capacity (a low capacity to store thermal energy) will have a greater temperature increase than those with a high specific heat capacity.

Apparatus required

Aluminium block with two holes, one for a thermometer and one for a heater
50 W, 12 V heater

Thermometer
Beaker (250 cm 3 )

Safety precautions

The heating element will get very hot, especially if not inside a metal block. Take care not to burn yourself
Damaged equipment should not be used (e.g. bare wires etc.)
If you scald yourself with the heater or water then, cool under running cold water immediately for 10 minutes.
Measure the mass of the aluminium block using the balance, if recorded in grams, this should be converted into kilograms.
Place the heater and thermometer into the aluminium block

Measure the starting temperature of the metal block (you may need to wait for the thermometer to stop changing first).
Turn the power pack on and up to about 5V, this can be higher for certain heaters (but it will say the maximum on it)
Record the ammeter and voltmeter readings every 60 seconds in a table like that shown further down this page. These values may vary during the experiment, but they shouldn’t do significantly. Whilst recording the ammeter and voltmeter reading, also record the new temperature of the block at each 60s interval.
After about 10 minutes turn off the power supply.
Keep the thermometer in the metal block for a while longer. Record the maximum temperature of the block. The heater will still have some energy after you have turned off the power supply so you want to record any additional temperature rise from this energy.

$P = IV$

Examples of results tables you should consider using:

Things to consider before experimenting

The heating element should fit very snuggly into the metal block, but there may be a small layer of air between the heating element and the metal block. Add a drop of water before you put the heating element in to improve transfer of energy between the heating element and the metal block.
Remember to measure the mass of the metal block. These blocks are usually 1kg, but to make sure your calculations are accurate, you should take an accurate mass measurement.
Make sure you heat the metal block for at least 10 minutes; otherwise you will not be able to draw a graph with a good range of results.
Don’t forget to use your graph to find the gradient of the line. You will need this and the mass of the block to work out the specific het capacity of the metal.

Analysing the results

After drawing you line of best and taking your gradient the specific heat capacity can be found by using the following equation:

$\text{specific heat capacity} = \frac{1}{mass \times gradient}$

Exemplar graph and results:

****waiting for a good graph to be drawn from a student ****

Usually, the value for specific heat capacity found is higher than it should be, this is because more energy is put into the system than that used to heat up the substance. Some energy goes into wasted energy, such as heat loss to the surroundings. To improve the results, an insulation material should be used around the block.
If you are trying to determine the specific heat capacity of a liquid, then the liquid should be stirred before each measurement to ensure all the water is the same temperature. Additionally, a lid should be used, since heat rises this is one way thermal energy can be lost to the surroundings.

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COMMENTS

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Method. Apparatus to investigate the specific heat capacity of the aluminium block. Start by assembling the apparatus, placing the heater into the top of the block. Measure the initial temperature of the aluminium block from the thermometer. Turn on the power supply and start the stopwatch.
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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.