# A2 /EXPT/THER/KELLY/APRIL

38 %
63 %

Published on October 10, 2009

Author: ramphy

Source: slideshare.net

Electric Method – Specific Latent Heat of Vaporisation of water by April and Kelly Oct, 10th

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.

Heat the beaker of water to its boiling point using a spirit burner. Then stop heating.

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.

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.

Steps –Part 3 Set up the electrical circuit as shown. Emerge the 50Ω resistance in the beaker of water.

Set up the electrical circuit as shown. Emerge the 50Ω resistance in the beaker of water.

Switch on and at the same time start the stopwatch. Note down the readings of the voltmeter and ammeter. Steps –Part 4

Switch on and at the same time start the stopwatch. Note down the readings of the voltmeter and ammeter.

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.

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.

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

m is the mass of vaporised water.

Q is the heat supplied to the boiling water.

Formula: L= Q/m =VIt/ m 2-m1.

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.

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.

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.

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.

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.

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.