❌ 1. Required Practical: Specific Heat Capacity (P2) Flashcards
Aims of this Practical
In this experiment, you will take measurements of energy transferred and temperature change and use these to find the specific heat capacity of Aluminium. You will measure: Mass, Work Done by the Heater, and Tenperature.
How Is SHC Involved In This Experiment
Objects of the same mass but made of different substances need different amounts of energy to raise their temperature by the same amount.
Each substance has its own specific heat capacity, which tells us how much energy is needed to raise the temperature of 1 kg of that substance by 1°C.
The equation for calculating a specific heat capacity from energy and temperature measurements is:
Specific Heat Capacity ‘c’ (J/kg°C) = Energy Transferred ‘ΔE’ (J) / Mass ‘m’ (kg) x Temperature Change ‘Δθ’ (°C)
Equipment for SHC Prcatical
- metal block wrapped in insulation, with two holes for a thermometer and heater
- thermometer
- pipette to put water in the thermometer hole
- 30 W heater
- 12 V power supply
- insulation to wrap around the blocks
- ammeter and voltmeter
- five 4 mm leads
- stop watch or stop clock
- balance
Health and Safety for SHC Practical
- do not touch electrical equipment, plugs, or sockets with wet hands
- do not touch the heater: it becomes very hot when in use, and can stay hot for
a long time after it is switched off - switch the heater off if you think it is overheating
- switch the heater off when you have finished using it
- when the thermometer is not being used, make sure it is placed where it cannot easily roll off the table.
Independant Variable for SHC Practical
The Independant Variable in this experiment is the Work Done (J). This is because it is the variable that changes throughout the experiment as the time goes on.
Dependant Variable for SHC Practical
The Dependant Variable in this experiment is the Temperature (°C). This is because this is the variable that is being tested against the work done to get the Specific Heat Capacity.
Control Variables for SHC Practical
The Control Variables in the experiment are that the same electrical wires should be used throughout the experiement, as well as keeping all of the electrical equipment the same (ensuring the resistance in the circuit is the same). You should also use the same thermometer, the same heater, along with the same amount/thickness of insulation. The most obvious control variable, however, is the time you take the readings for.
Method for SHC Practical
- Obtain metal block (1 kg).
- Place a small amount of glycerine (we used water) in the larger hole in the block and insert the heater.
- Connect the ammeter, power pack and heater in series.
- Fully insulate the block by wrapping it loosely with cotton wool, for example.
- Connect the voltmeter across the power pack in parallel.
- Put a small amount of glycerine (we used water) in the small hole.
- Put the thermometer in this hole.
- Switch the power pack to 12 V. Switch it on.
- Record the ammeter and voltmeter readings. These shouldn’t change during the experiment.
- Measure the temperature and switch on the stop clock.
- Record the temperature every minute for 18 minutes. Add your results to the results table.
Sources Of Inaccuracy (And How To Counteract Them)
- Thermal Energy can pass out of the beaker into the air (Use an insulator with a lower thermal conductivity)
- Not all thermal energy passes into the oil (Ensure that the immersion heater is fully submerged)
- You can reader the thermometer incorrectly (Use an electronic temperature probe)
- Thermal energy not being fully spread through the water, for example (You can stir the water to ensure the water is a consistant temperature throughout)
How to lay out the Results Table
The table consists of 3 colums, on the left is the ‘Time in Seconds’, in the middle is ‘Work done in J’ and on the right is the ‘Temperature in °C’.
To get the work done, you need to calculate the Power x Time. To get power, you follow the equation the equation Power = Current (amps) x Voltage (volts).
How to lay out the Graph
On the X-Axis was the ‘Work done in J’, and on the Y-Axis was the ‘Temperature in °C).
The line drawn the graph was of a postive correlation, meaning the temlerature increased as the work done increased.
How to Calculate the Specidic Heat Capacity
Firstly you find out the gradient of the graph showing the temperature against the work done. In doing this you have to calculate:
Change in Y / Change in X
Once you have the gradient, you work out the Heat Capacity by doing the equation:
1 / Gradient
Why will the SHC value calculated be a little more than in reality
The reason why the Specific Heat Capacity that I calculated will be higher than the actual one is because some of the power going to the heater was being lost to the surroundings through various different ways, but the main one was that, nearly half of the heater was sticking out of the metal cylinder. This would’ve meant that more energy were used compared the to amount fo energy that was actually needed, which is why this SHC will be higher.
Does Volume affect SHC
This is not true for the blocks I tested, because the volume does not change specific heat capacity for any object. This is because specific heat capacity is only dependant on the material of the object itself, meaning it’s independant (not changed by) of it’s mass or volume, shown by the calculations above.
