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# A2 /EXPT/THER/KELLY/APRIL

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### Transcript

• 1. Electric Method – Specific Latent Heat of Vaporisation of water by April and Kelly Oct, 10th
• 2. Steps – Part 1
• Add some water into a beaker to about three quarters full.
• Heat the beaker of water to its boiling point using a spirit burner. Then stop heating.
• 3. Steps – Part 2
• Place the beaker in a calorimeter to prevent heat entering to leaving. Leave a hole at the top to let steam out.
• Weigh it using an electronic balance. Note down the mass m1.
• 4. Steps –Part 3
• Set up the electrical circuit as shown. Emerge the 50Ω resistance in the beaker of water.
• 5.
• Switch on and at the same time start the stopwatch. Note down the readings of the voltmeter and ammeter.
Steps –Part 4
• 6. Steps –Part 5
• After some time when at least half of the water has vaporised, switch off and note down the time t of the current flowing.
• Weigh the beaker, calorimeter and water again. Note down the mass m2.
• 7. Tabulation and Calculation
• m is the mass of vaporised water.
• Q is the heat supplied to the boiling water.
• Formula: L= Q/m =VIt/ m 2-m1.
m=m 2-m1/g m 2/g m 1/g Q=VIt /J t/s I/A V/V
• 8. Sources of Errors
• The weighing of the beaker of water after being heated to its boiling point may take some time and cool the water a bit.
• The electrical resistance is much colder than boiling water and when emerged in it, it will absorb some heat.
• During the electrical heating, water vapour may liquefy again touching the cold lid of the calorimeter and drop back into the beaker.
• 9. Improvements
• Weigh the beaker of water quickly when it’s hot.
• Switch on the circuit before the resistance is emerged in water for some time to heat it up. Try to use a small electrical resistance.
• Heat the calorimeter lid for a while (no touching) before it is used.
• 10. Safety Precautions
• Take care not to split any drops when moving hot water.
• Be careful about the fire of the spirit burner.
• Pay attention not to split water on wires and power supply.