Investigating Specific Heat Capacity (Cambridge (CIE) O Level Physics): Revision Note

Investigating Specific Heat Capacity

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 Measure Specific Heat Capacity

Apparatus to investigate the specific heat capacity of the aluminium block

1. Start by assembling the apparatus, placing the heater into the top of the block

2. Measure the initial temperature of the aluminium block from the thermometer

3. Turn on the power supply and start the stopwatch

4. 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

5. Switch off the power supply, stop the stopwatch and leave the apparatus for about a minute. The temperature will still rise before it cools

6. Monitor the thermometer and record the final temperature reached for the block

• An example table of results might look like this:

Example Results Table

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:

$∆E=mc∆\theta$

• Where:

  • ∆E = 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)

  • ∆θ = change in temperature, in degrees Celsius (°C)

• Rearranging for the specific heat capacity, c:

$c=\frac{∆E}{m∆\theta }$

• To calculate ∆θ:

$∆\theta =\text{final temperature}-\text{initial temperature}$

• To calculate ∆E:

$∆E=IV{t}_f-IV{t}_i$

• Where:

  • I = average current, in amperes (A)

  • V = average potential difference (V)

  • t_f = final time, in seconds (s)

  • t_i = 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

• Make sure the voltmeter and ammeter are initially set to zero to avoid zero error

• 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 20 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