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Thermal Physics

2TP

Experiment to measure the Specific Latent Heat of Vaporisation of Water

1. Preparation: a) Learn the definition of specific latent heat.
b) It is usually found to be easier to measure the quantity of heat given out when steam condenses than to measure the quantity of heat needed to vaporise water. (To see that this is true, try to design an experiment in which you measure the quantity of heat needed to vaporise 1kg of water.)
c) See part 3 below.
2.

Set up apparatus as shown in the diagram below; it might be convenient to use rubber tubing for the delivery tube. Be careful, it will get HOT !

The experiment consists of passing the steam (assumed to be at 100C) through cold water where (some of) it will condense.

Heat the water to boiling point and leave it boiling for a few minutes before putting the container of cold water in place.

3. a) Why must you wait for a few minutes before putting the container of cold water in place? How will you know when the apparatus is ready for use?
b) Derive an equation which will allow you to calculate the specific latent heat of vaporisation of water from your results. Think about the main sources of error in an experiment like this and how to reduce the effects of these errors on the precision of the final result.

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