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The specific latent heat of vaporisation of water can be determined using the apparatus shown - Edexcel - A-Level Physics - Question 3 - 2023 - Paper 3
Question 3
The specific latent heat of vaporisation of water can be determined using the apparatus shown. (a) A student planned to vary the current in the heater from 0 A to 5... show full transcript
Worked Solution & Example Answer:The specific latent heat of vaporisation of water can be determined using the apparatus shown - Edexcel - A-Level Physics - Question 3 - 2023 - Paper 3
Step 1
Criticise the student's circuit.
Answer
The ammeter should be in series with the heater to accurately measure the current flowing through it. If the ammeter is not correctly positioned in the circuit, it won't measure the current properly. Additionally, the range of the ammeter (in mA) may be too small; this could lead to inaccurate readings if the current exceeds this range. Both axes of the circuit should be labeled for clarity.
Step 2
Sketch a graph, on the axes below, of how the readings on the balance would vary with time.
Answer
The graph is expected to show a straight line with a negative gradient, indicating that the mass of water in the beaker decreases over time as the water boils away. The readings should start high and gradually decrease, illustrating the loss of mass due to vaporisation.
Step 3
Calculate the specific latent heat of vaporisation of water, L.
Answer
Using the formula for energy:
Where:
- Voltage, V = 12 V
- Current, I = 4.2 A
- Time, t = 6.0 minutes = 6.0 × 60 = 360 seconds.
Calculating the energy:
Now, the mass of water (m) lost is 7.5 g = 0.0075 kg. The specific latent heat, L, is calculated as:
Step 4
Explain how another significant source of error affects the value of L obtained from the experiment.
Answer
Energy is transferred from the beaker and water to the surroundings, which could lead to an inaccurate measurement of the latent heat. Additionally, if there are inconsistencies in measuring the time taken for boiling or fluctuations in boiling conditions, this can result in a value of L that is larger than the true value, affecting the overall accuracy of the experiment.