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# A2 /EXPT/THER/KELLY/APRIL

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### A2 /EXPT/THER/KELLY/APRIL

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