Safety
The teacher has informed me that the one safety issue is to ensure that when the heater is on it is in water otherwise the heater will over heat and burn out. This is dangerous because it could potentially cause a fire. The danger of this heater is great, so the plastic cup is placed in the beaker to stabilise it, so to prevent the cup being knocked over and the heater burning out.
Predictions
I predict that when varying the mass of the water. As the mass of water rises the temperature of the water will be lower after the given time of 4 minutes. I also predict that when the mass of water doubles the temperature rise will half.
My predictions have been made on my previous knowledge of heating and shall be explained below:
Energy Supplied = Mass x Specific Heat Capacity of Water x Temperature Rise
Knowing that- Power x Time = Energy. And that Amps x Volts = Power, I can say that:
Amps x Volts x Time = Mass x Specific Heat Capacity x Temperature Rise
The following symbols will now be used:
V = Volts
I = Amps
T = Time
M = Mass
S = specific heat capacity
∆t = temperature rise
I have already stated that:
IVt = mS∆t
I am varying the mass of water therefore: I, V, t and S are fixed. If the formula is rearranged in the form of ∆t being the subject then I am given:
∆t = IVt
mS
Knowing that I, V , t and S are fixed they can be removed from the formula. I am thus left with:
∆t 1
m
This is where my prediction came from. This basic theory does not take into account heat loss to air or energy absorbed by the cup.
Apparatus
The following apparatus is needed:
- Variable Power Supply
- Beaker
- Polystyrene Cup
- Heater
- Electrical Leads
- Ammeter
- Volt Meter
- Thermometer
- Timer
- Water
The apparatus will be set up as follows:
Method
The apparatus has been shown above; the method for carrying out this experiment will now be explained. Once the experiment has been set up as shown above, a cup should be placed on the scales and filled with the relevant amount of water. Remember to ‘zero’ the scales first to remove the weight of the cup. The cup is then placed in the beaker and the heater is submerged in the water. The thermometer is placed in the water and left for 1 minute to adjust to the water temperature. The initial water temperature is taken off the thermometer. The power supply will then be turned on and set to 3 Amps and 4.4 Volts. Immediately the timer is started. The timer is left running for 4 minutes, during which time the water is stirred intermittently every 20 seconds with the thermometer. When the timer reaches 4 minutes the power is switched off, and the water is stirred for another 20 seconds because the heater will still be producing heat. The reading will be taken off the thermometer and recorded on paper. The results will then be put into a graph and then analysed. For the next reading to be taken the thermometer is placed in the new mass of water for about 1 minute so that it can adjust to the temperature of the new water. Once it has adjusted the reading is taken and then the power supply is again turned on and the process is repeated.
Obtaining My Evidence
The experiment was carried out as in the method section above all the details of how the experiment was carried are explained. Everything went as hoped there were no major misjudgements of the method.
Table to Show the Results of the Experiment of Water Being Heated Electrically and Varying the Mass of Water
Abc=Anomalous Results
Analysis Of Evidence
The graphs I have shown were best drawn as a line graphs as you can see on the following pages. The graphs on the following pages show a clear declining curve. The graphs show that the temperature rise of water is proportional to the mass of water that is heated. The graph follows a straight line until reaching the mass of 90g where it begins to level off. The line of best fit I have drawn clearly shows the direction of which the graph is trying to create. One anomaly has occurred, at 110g the temperature rise seems to be greater than that at 100g of water. This is slightly puzzling as surely the temperature rise should decrease because there is more water to heat in the same amount of time.
The pattern these results have shown is that as the mass of water increases the temperature rise decreases. This is shown on both graphs by the lines of best fit.
In my prediction I stated that as the mass of water increased the temperature rise would decrease. This qualative prediction has proven to be correct. My second prediction was a quantative prediction which stated that as the mass of the water doubled the temperature rise would half. This unfortunately has not been proven correct. The results do as I have said support the prediction that as the mass of water increases the temperature rise will decrease. This has been shown on the graphs. The line of best fit shows that the mass of water is proportional to the temperature rise and that they are inversely proportional so as one rises the other decreases.
The results have shown that my prediction was correct, that as mass of water increases the temperature rise will decrease. I have discovered that the two factors are inversely proportional. My results can be backed up with the science I used to make my prediction. When the constant factors are removed from the formula it is left that the temperature rise is proportional to the mass of water. All of which was explained in the planning section of this coursework. There is more science to this experiment though.
I now know that the mass of water is proportional to the temperature rise, but why. It is because of the way heat travels. Heat is a vibration, water molecules vibrate and the more they vibrate the hotter they become. While vibrating they hit other atoms and cause them to vibrate hence the heat travels through the water. Water has a special way of transferring the heat, heat travels either by radiation like in radiators, conduction like when a sauce pan is placed on an oven and the handle gets hot or convection as in water. Convection currents as they most commonly occur happen when a heat source heats water. This heated water rises to the top of its container where it cools and then falls again. A current is set up and the water moves in a circle around its container. In time the water gets hotter as a whole. As the water rises to the top of its container it loses a lot of its heat energy to the other particles so by the time it begins to sink again it is no longer heating other particles. This explains why when there is a larger amount of water it takes longer for the water molecules to rise to the top of the container therefore they get cooler quicker meaning that a smaller percentage of the water molecules in the larger container get heated. To put it in simple terms it simply comes down to the fact that when there is more water to heat it takes longer because there is more of it. There are a greater number of water molecules to heat up and so it takes longer to heat them all up. So if I am trying to heat all the different water mass to the same temperature they will all take different lengths of time, I am measuring the temperature rise over a given time, thus the temperature rise will not be as great for the bigger masses of water because the heat is spread out throughout all the particles and in general the water is not as hot as the water with a small mass.
Evaluation
Improvements
There are some ways I fell I could improve the way the experiment was carried out because there are a lot of reasons for the anomalous results which can and should have been removed now that they have become apparent.
Firstly I think that the cup should have had some sort of lid to prevent heat loss through evaporation. In the experiment I carried out the cup was left open and a lot of heat was doubtlessly be lost to the atmosphere thus hindering the accuracy of my results.
Secondly the cup, the cup was polystyrene this meant although it is a reasonable insulator some heat will have been lost to the cup. Possibly to reduce this inevitable heat loss, the cup could have a shiny silver lining to reduce heating by radiation.
Although these improvements have been made the results I received were accurate. The timer that was used in the experiment was accurate to 1/100th of a second and so the timer told me exactly when to stop the power. This meant that the test was fair and that results wouldn’t vary in accuracy. The thermometer was accurate to ½ a degree Celsius so there was no dilemma with accuracy on that account. The weighing scales were also accurate to 1/100th of a gram so that the water masses could be very accurate, this ensured a fair test.
The results are reasonably reliable. The results used in the graphs were averages so that any chance of anomalies is hopefully removed. Providing that the same equipment is used and that the test is carried out in the exact same way as I have carried out I am sure that the same results would be received.
Evaluation
There was one result that did not fit with the rest of them, the result for a mass of water, of 110 grams. Supposedly the graph should continually go down as the mass increases the temperature rise should decrease this has been proven by are results to be correct. This anomaly is puzzling. The reason for the rise in temperature rise can be explained in many ways. The main reason I believe is that, when a big mass of water is used the temperature rise is so small that even the slightest variation in the experimental procedure could affect the results. Heat loss to air, heat loss to the cup, stirring the water, and impurities in the water could all make variations in the heating. With all these factors to consider it is not surprising that an anomalous result has occurred.
Even so I believe that my results are good enough to draw a firm conclusion from. They are all reliable and accurate, even with the anomaly my prediction was correct and the line of best fit proves my results to be accurate. I can trust my results because the experiment was carried out with professionalism and accuracy to ensure a safe, fair test. I therefore trust my results to be accurate and correct.
Further Work
There are a few opportunities for further work including the 2 other experiments mentioned in my planning section. I could test the effect of varying the power of the heater while heating water. This would link up with my experiment and provide me with extra knowledge. Also carrying out the third experiment on varying time would provide me with interesting information which would further extend my investigation.
Another experiment that I think would be interesting is varying impurities in the water and discovering how impurities affect the time taken to heat water.
