Investigating the specific heat capacity
In a nutshell
By recording the temperature of materials as they change, the specific heat capacity of each material can be investigated. You will do this by conducting two experiments. One will look at the energy supplied to change the temperature of blocks of metals over a period of time and the other will look at the energy supplied to change the temperature of water over a period of time.
Equations
Word Equation | Symbol Equation |
change in thermal energy=mass×specific heat capacity×change in temperature | ΔE=m×c×Δθ |
thermal energy=current×potential difference×time | E=I×V×t |
Note: Δ means 'change of' which is the difference between the final and initial value.
Variable definitions
Quantity Name | Symbol | unit name | Unit |
thermal energy | | | |
| | kilogram | |
specific heat capacity | | joule per kilgram per degree Celsius | J/kg°C |
temperature | | degree Celsius | |
| | | |
potential difference | | | |
| | | |
Equipment list
The following equipment list can be used to conduct the experiment to investigate the specific heat capacity of different materials.
Equipment | Use |
1kg blocks of copper, iron and aluminium, with two holes in each | To find the specific heat capacity of. |
Thermometer | To measure the temperature. |
Pipette | To add a drop of water in the thermometer hole. |
Insulation | To wrap around the materials to prevent heat loss. |
12V immersion heater | To heat the materials. |
12V power supply | To provide power to the immersion heater. |
Stopwatch | To time the experiment. |
Ammeter and Voltmeter | To find the power of the heater by measuring the potential difference and current through the heater. |
Five connecting leads | To connect the power supply, ammeter, voltmeter and immersion heater. |
Water | To find the specific heat capacity of. |
400ml beaker | To hold the water. |
Note: If the mass of the blocks are unknown, also include a digital balance to find the mass.
Experimental variables
The independent variable is the variable you change. The dependent variable is the variable that changes depending on the other variables, and is the one you measure. The control variables are the variables that are kept constant.
Independent Variable | |
Dependent Variable | Temperature |
Control Variables | Same material for each set of measurements, current supplied, potential difference supplied |
Safety precautions
When performing experiments, it is very important to consider safety precautions. This is so that no one gets hurt or injured during the experiment.
Hazard | Risk | Safety Measure |
Heater | Touching the heater whilst it is on or just after it is switched off could result in burns. | Don't touch the heater whilst it is still hot. If burnt, run the burn under cold running water for five minutes. |
Hot equipment | The equipment (heater, block, wire etc.) will remain hot for a while after it has been used. | Don't pack away immediately, wait until the equipment has cooled. |
Water and electrics. | Water mixing with the electrical equipment could cause it to break or start a fire. | Keep the water away from all electrical equipment. |
Method
These are the instructions to complete the experiment. Record all measurements taken as you work through the experiment in a table.
| 1. | Thermometer | 2. | Metal block | 3. | Immersion heater | 4. | Voltmeter | 5. | Ammeter | 6. | Power supply | |
1. | Set up the apparatus as shown in the diagram. Wrap the insulation around the base and sides of the block. |
2. | Drop water inside the thermometer hole and place the thermometer in this hole. |
3. | Measure the initial temperature of the block and start the timer. |
4. | Switch the power supply on at 12V and record the ammeter and voltmeter readings. Note: The voltmeter and ammeter readings should not change during the experiment. |
5. | Record the temperature measured by the thermometer every minute for 10 minutes. |
6. | Repeat steps 1-5 for each other metal block. |
Analysis
This is how you will use the data recorded to form conclusions.
1. | For each measurement of the temperature, calculate the work done by the heater. This is done by using the thermal energy equation thermal energy=current×potential difference×time E=I×V×t Note: The power of the heater can be found using P=I×V. This is what the equation above is derived from. |
2. | Plot a graph of the temperature of each metal block against the work done. Draw a line of best fit for each line for this graph. |
3. | Calculate the gradient of all your lines of best fit. Tip: The beginning of your graph may be curved so ignore this part when finding each gradient of the line. |
4. | Use the gradients of the graph to calculate the specific heat capacity of each block. As the mass is equal to 1kg, this is done by using the formula specific heat capacity,c=gradient1
Note: If the mass of the block you used was not equal to 1kg, you will have to divide by the mass to find the specific heat capacity. You can check this by considering the units of the equation. |
Conclusion
| A. | Temperature of the metal block ( °C) | B. | Work done by the heater ( J) | The horizontal and vertical lines are used for calculating the gradient. |
The graph from the measured values of the experiment should look similar to this. The copper line should be the steepest as it has the lowest specific heat capacity. The aluminium line should be the least steep as it has the highest specific heat capacity. This means it takes less energy to change the temperature of aluminium than it does to change the temperature of copper by the same result.
Evaluation
Once you have completed your experiment, it is important to consider how it could be improved. You should come up with ways to improve the accuracy of your values. If you got a result that seems unreasonable, think about why this was.
Experiment 2: Investigating the specific heat capacity of water.
Experimental variables
The independent variable is the variable you change. The dependent variable is the variable that changes depending on the other variables, and is the one you measure. The control variables are the variables that are kept constant.
Independent Variable | |
Dependent Variable | Temperature |
Control Variables | Water, current supplied, potential difference supplied |
Safety precautions
When performing experiments, it is very important to consider safety precautions. This is so that no one gets hurt or injured during the experiment.
Hazard | Risk | Safety Measure |
Heater | Touching the heater whilst it is on or just after it is switched off could result in burns. | Don't touch the heater whilst it is still hot. If burnt, run the burn under cold running water for five minutes. |
Hot equipment | The equipment (heater, wire etc.) will remain hot for a while after it has been used. | Don't pack away immediately, wait until the equipment has cooled. |
Water and electrics. | Water mixing with the electrical equipment could cause it to break or start a fire. | Try your best to isolate the electrics from the water. |
Method
These are the instructions to complete the experiment. Record all measurements taken as you work through the experiment in a table.
| 1. | Thermometer | 2. | Metal block | 3. | Immersion heater | 4. | Voltmeter | 5. | Ammeter | 6. | Power supply | |
1. | Place the beaker on the digital balance and reset the balance to zero. This makes sure the mass of the beaker isn't included in the mass of the water. |
2. | Fill the beaker with 250ml of water and measure the mass. |
3. | Set up the apparatus as shown in the diagram. Place the immersion heater and and thermometer in the water. |
4. | Record the initial temperature of the water using the thermometer and start the timer. |
5. | Switch the power supply on at 12V and record the ammeter and voltmeter readings. Note: The voltmeter and ammeter readings should not change during the experiment. |
6. | Record the temperature measured by the thermometer every minute for 10 minutes. |
Analysis
This is how you will use the data recorded to form conclusions.
Follow the same procedure as the previous experiment. When calculating the specific heat capacity, you will have to divide the reciprocal of the gradient by the mass of the water.
c=gradient×mwater1
Conclusion
| A. | Temperature of the water ( °C) | B. | Work done by the heater ( J) | 1. | Line of best fit |
|
The graph from the measured values of the experiment should look similar to this. The specific heat capacity of water is 4200J/kg°C to two significant figures. The calculation made from the gradient from your graph should be around this value.
Evaluation
This is the same as the previous experiment.