Done by: Khoo Chun Yuet (3S306)
Activity
Pupils try to lower the temperature of water as much as possible without adding anything
to the water or decreasing the volume of water.
Apparatus
1.
2.
3.
4.
5.
6.
A black and large metal container
Fan
Thermometer
Stop watch
Retort stand
500ml of water at 80C
Venue:
1. We should carry out the experiment preferably in places with higher altitude. In
the context of Singapore where there are few places that are high above sea level,
we can perhaps carry out the experiment on the highest storey of a skyscraper etc
but the effect may be minimal.
2. We should also carry out the experiment in a very cold environment so that the
temperature gradient between the surroundings and the hot water is greater to
increase thermal energy loss to the surroundings and for the water to achieve
thermal equilibrium with the surroundings at a lower temperature (maybe only,
because 3 minutes may be too short a time for the water to reach thermal
equilibrium with the surroundings).
Hypothesis:
The cooling rate of the water increase when there is a larger temperature gradient
between the water and the surroundings, when the outside atmosphere is windy, when the
water has a larger surface area in contact with atmospheric air, when the container is a
good emitter of radiant energy and when the air pressure surrounding the water is low.
Experimental procedure:
1. Identify an area with high altitude to carry out the experiment.
2. Switch on the fan and ensure that it is blowing towards the direction where the
set-up is placed.
3. Clamp the thermometer tightly onto the retort stand.
4. Position the thermometer where it is suspended in the container to ensure that the
bulb of the thermometer is completely submerged in hot water.
5. Pour the 500ml of water at 80oC into the container.
6. Start timing immediately and record the temperature of the boiling water at
intervals of 15 seconds until 3 minutes is over.
Post experiment procedure to measure the effect of the change to obtain reliable
results:
Tabulate the readings in the form of a table and use the information to plot a graph of
temperature against time (preferably using Microsoft excel).
To obtain more accurate results to minimize human error, perform the experiments in
triplicates.
Explanation for set-up:
A black and large metal container is used.
1. Firstly, I had learnt in physics lesson that black surfaces are good emitters of
radiant energy. To prove this, we can conduct another experiment comparing the
thermal energy emitted by black and silvered surfaces.
2. Secondly, metals are also good emitters of heat energy. In this experiment, the
material to be used should rightfully be silver because silver is the best emitter of
thermal energy among all metals and it can allow the water to cool fastest in three
minutes. Since the experiment did not state the budget of the experiment, we will
be using silver.
3. Next, the container should be large in the sense that optimally, the container has a
large length and breadth with a shorter height. This is so as to increase the surface
area of the water in contact with the atmosphere to maximize thermal energy loss
to the surroundings.
A fan is used.
1. As we all know, the temperature of the water is relatively high at 80C and the
water molecules have a greater average kinetic energy. The rate of evaporation
thus increases. This is good as evaporation will reduce the temperature of the
boiling water as the average kinetic energy of the water molecules will decrease.
However, as water evaporates, it will cause the still air just above the water
surface to be more humid. Humidity will then result in the water losing heat to the
surroundings slower. Therefore, a fan is used to aid in the movement in air to
blow away the diffusion shell and maintain the temperature gradient of the hot
water with the surroundings.
2. The fan is also used to lower the temperature of atmospheric air.
A thermometer is used:
It is used to measure the temperature of water at regular intervals of 15seconds.
A stopwatch is used:
To indicate intervals of 15seconds and to make sure that the measurement of the set-up’s
temperature does not exceed 3 minutes.
A retort stand is used to clamp and support the thermometer.
Limitations:



When pouring the water into the container, some of the thermal energy of the hot
water is already loss to the surroundings.
There is human reaction time error for recording exact 3 minutes.
A high altitude environment may not be easily accessible in Singapore.
Improvements:
Use a data logger to obtain more reliable results.
Perform the experiments many times to reduce human error.
Perform the experiment in another country.
Conclusion:
The temperature of water decrease when there is a larger temperature gradient between
the water and the surroundings, when the outside atmosphere is windy, when the water
has a larger surface area in contact with atmospheric air, when the container is a good
emitter of radiant energy and when the air pressure surrounding the water is low.