Required Practical: Investigating Specific Heat Capacity (AQA GCSE Combined Science: Trilogy: Physics): Revision Note

Required Practical 1: 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 amount of energy transferred to the substance with the rise in temperature of the substance

Variables:

• Independent variable = Time, t

• Dependent variable = Temperature, θ

• Control variables:

  • Material of the block

  • Mass of the block, m

  • 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

• Note: Resolution is the smallest change an instrument can show (the scale division) and is different from the range of the scale

Method

Apparatus to investigate the specific heat capacity of the aluminium block

1. Measure the mass of the aluminium block using a balance

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

3. Leave the thermometer in the block for a few minutes so that it reaches the same temperature as the block, then measure the initial temperature

4. Turn on the power supply and start the stopwatch

5. Whilst the power supply is on, the heater will heat up the block. Take several periodic measurements, e.g. 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

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

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

8. Record the temperature at regular intervals (e.g. every minute) and plot a temperature–time graph

• For the water variant, measure the mass of the empty beaker, add water and measure the mass again, then calculate:

Mass of water = total mass − mass of beaker

• An example table of results might look like this:

Analysis of Results

• The thermal energy supplied to the block can be calculated using the equations:

$E=QV$ and $Q=It$

• Where:

  • E = thermal energy, in joules (J)

  • Q = charge, in coulombs (C)

  • I = current, in amperes (A)

  • V = potential difference, in volts (V)

  • t = time, in seconds (s)

• To combine the equations, first rearrange E = QV to make Q the subject

$Q=\frac{E}{V}$

• Substitute this into the Q = It equation

$\frac{E}{V}=I\times t$

• Rearrange to make E the subject

$E=I\times V\times t$

• The change in thermal energy is defined by the equation:

$∆E=m\times c\times ∆\theta$

• Where:

  • ∆E = change in 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:

$c=\frac{∆E}{m\times ∆\theta }$

• To calculate ∆θ:

$∆\theta ={\theta }_f-{\theta }_i$

• Where:

  • θ_f = final temperature

  • θ_i = initial temperature

• To calculate ∆E:

$∆E=IV{t}_f-IV{t}_i$

• Where:

  • I = average current, in amperes (A)

  • V = average potential difference, in volts (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

• Comparing your result with the accepted value:

$\text{percentage difference}=\frac{\text{your value}-\text{accepted value}}{\text{accepted value}}\times 100$