Investigating Specific Heat Capacity (Extended)
EXTENDED
Aims of the Experiment
- The aim of the experiment is to determine the specific heat capacity of a substance, by linking the decrease of one energy store (or work done) to the increase in temperature and subsequent increase in thermal energy stored
Variables:
- Independent variable = Time, t
- Dependent variable = Temperature, θ
- Control variables:
- Material of the block
- Current supplied, I
- Potential difference supplied, V
Equipment List
- Resolution of measuring equipment:
- Thermometer = 1 °C
- Stopwatch = 0.01 s
- Voltmeter = 0.1 V
- Ammeter = 0.01 A
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
- Whilst the power supply is on, the heater will heat up the block. Take several periodic measurements, eg. every 1 minute of the voltage and current from the voltmeter and ammeter respectively, calculating an average for each at the end of the experiment up to 10 minutes
- Switch off the power supply, stop the stopwatch and leave the apparatus for about a minute. The temperature will still rise before it cools
- Monitor the thermometer and record the final temperature reached for the block
- An example table of results might look like this:
Analysis of Results
- The thermal energy supplied to the block can be calculated using the equation:
E = IVt
- Where:
- E = thermal energy, in joules (J)
- I = current, in amperes (A)
- V = potential difference, in volts (V)
- t = time, in seconds (s)
- The change in thermal energy is defined by the equation:
ΔE = mcΔθ
- Where:
- ΔE = change in thermal energy, in joules (J)
- m = mass, in kilograms (kg)
- c = specific heat capacity, in joules per kilogram per degree Celsius (J/kg °C)
- Δθ = change in temperature, in degrees Celsius (°C)
- Rearranging for the specific heat capacity, c:
- To calculate Δθ:
Δθ = final temperature – initial temperature
- To calculate ΔE:
ΔE = IVtf – IVti
- Where:
- I = average current, in amperes (A)
- V = average potential difference (V)
- tf = final time, in seconds (s)
- ti = initial time, in seconds (s)
- These values are then substituted into the specific heat capacity equation to calculate the specific heat capacity of the aluminium block
Evaluating the Experiment
Systematic Errors:
- Make sure the voltmeter and ammeter are initially set to zero, to avoid zero error
Random Errors:
- Not all the heat energy supplied from the heater will be transferred to the block, some will go into the surroundings or heat up the thermometer
- This means the measured value of the specific heat capacity is likely to be higher than what it actually is
- To reduce this effect, make sure the block is fully insulated
- A joulemeter could be used to calculate energy directly
- This would eliminate errors from the voltmeter, ammeter and the stopwatch
- 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
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 the equipment
- Keep water away from all electrical equipment
- Wear eye protection if using a beaker of hot water