We must also understand that there is going to be some change in the mass of the water, due to evaporation, so we will measure the mass of the water before and after the experiment so we are able to take this into account.
We are planning to repeat the experiment 3 times over 5 minute periods, measuring the temperature of the water every minute, and then make an average result. We are doing this to increase accuracy and also because if we were to do the experiment in one long period, the temperature rise would be too large and that would increase the amount of heat being lost, so it would ultimately lead to inaccuracy.
Apparatus: A power pack, wires, a voltmeter, an ammeter, an immersion heater, a beaker, 200ml of water, a retort stand, a thermometer, a stop watch and some scales.
Method: This is the experiment we intend to carry out in order to obtain our results:
▪ Connect an immersion heater to a power pack in a circuit including a voltmeter and ammeter.
▪ Fill a beaker up with 200ml of water, and measure it’s mass.
▪ Put the heater in a retort stand so it stays in a fixed position, and place the heater in the water.
▪ Place the thermometer in the water and record the starting temperature.
▪ Switch on the heater and the stopwatch at the same time
▪ Also record the initial reading on the voltmeter and ammeter.
▪ Stir the water throughout the experiment, and record the temperature of the water every minute, for 5 minutes.
▪ After the experiment is complete, measure the mass of the water again.
The above is a diagram of how we will set up the equipment.
There are not many particular safety precautions that need to be taken, apart from the obvious- being careful with electricity, preventing the water from coming into contact with the wires and being careful when clearing away, as the heater will be hot.
I predict that our result for the specific heat capacity of water will be around 4600J/kg/OC. I know already that the specific heat capacity of water is supposed to be 4200J/kg/OC, but I am taking the heat loss into account. I would have predicted a higher value if it was not for 2 reasons:
- We are not using pure water, but tap water, and when salts are present, the specific heat capacity of water decreases slightly.
- During the experiment, some of the water will evaporate.
We have not studied specific heat capacity in great detail before
this experiment, but we were taught the formula. Our previous work on heat transfer helped me, and I also used the text book ‘The World of Physics’ by John Avison.
Results
Evaluation
The aim of the experiment was to find the specific heat capacity of water. We have worked that out to be 4480J/kg/oC. The result is much like what I expected and I am very pleased with our result. I think the experiment was quite successful. However, there were many areas in which we could have improved the experiment, because although the result is close to what I expected, it is not as close to what we know the real value of specific heat capacity of water is (4200J/kg/oc), so is quite simply not accurate enough.
Experiment Method Criticism: To start with, I think that I have to criticise the actual method of the experiment. I do not think the method was very good. I think the experiment may have been accurate, as in all the equipment was precise and as accurate as could be expected. But I do not think the experiment was very reliable. We can see form our results, that even though we only repeated it 3 times, each time our result was very different. This is probably due to human error, but I think we have to criticise the experiment and assume that in this way it is not reliable.
I think the experiment was definitely not suitable. I think the fact that it was set up in such a way that there was always going to be a large amount of heat loss through the beaker (via conduction), surface of water (via convection and radiation) and the heater (via convection and radiation), meant that the experiment was never going to be suitable. All this heat loss is what made the result for specific heat capacity of water higher than it should be.
Also, the experiment allowed water to evaporate, which would make the result of specific heat capacity lower.
I think that if I had the opportunity to do the experiment again, I would not. That is because I feel that we performed the experiment to an acceptable level of accuracy. However, I would perform a slightly different experiment that may produce even more accurate results. Here are the things I would change:
● I would wrap the beaker in cotton wool or something, so it insulates the beaker and prevents so much heat loss through the beaker, via conduction.
● I may use a different container for a beaker, made out of a material that does not conduct heat so well, another way of reducing heat loss.
● I would place the heater fully in the water, so no part of it is in the air, to reduce heat loss from the heater, via convection and radiation.
● I would put some form of lid on top of the beaker, to reduce heat loss from the surface of the water via radiation and convection.
All these changes would reduce heat loss, and cause the value of specific heat capacity lower, so make it more like what it should be.
Overall, I think our result was as good as it could be expected with the method of the experiment that we used. However, I think it would be interesting if we could perform a slightly different experiment, without the flaws in method of this one, and I am sure our result would be very accurate.
