Kettle 2 PDF

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Risk assessment I have understood and followed the recommendations in the risk assessment on Moodle.

Results Volume(L)= Mass (kg)1 0.8 1.0 1.2 1.6 1.7

Time 1 (s)

Time 2 (s)

Time 3 (s)

140.67 175.61 216.09 267.02 278.44

136.43 170.64 220.07 260.04 275.61

144.26 181.66 218.91 261.93 274.73

Average time (s) 140.45 175.97 218.36 263.00 276.26

Analysis of results: 1). Uncertainty in the average time: [(longest time – shortest time)/2] (s) 0.8L: 3.92s 1.0L: 5.51s 1.2L: 1.99s 1.6L: 3.49s 1.7L: 1.86s smallest increment = 0.100L Uncertainty of water = 0.100/2 = 0.05L Uncertainty of time = 0.01/2 = 0.005s

Time vs Volume

2). Graph

Time (s)

300.0 250.0

Equation of line of best fit: y = 148x + 28.5

200.0

Equation of max gradient line: y = 169x – 3.24

150.0

Equation of min gradient line: y = 136x + 39.5

100.0 50.0

0

0.0 0.0

2.0

4.0

6.0

Volume (L)

8.0

10.0

12.0

Kettle wattage = 1850-2200W  2025W (middle of the power range) Assume the initial temperature of the water is 25o C ΔT will always be 100-25=75o C

3).

Questions: 1). Why is it not safe to turn on the kettle without the element in the kettle being fully submerged? This is because if the heating coil is not submerged in water, the exposed part will not be able to transfer the energy to the water. The energy will then remain in the coil and the temperature of the coil will keep increasing (well over 100 degrees). This might be dangerous when someone is in contact with the coil. Also, this might cause a short circuit and we will not be able to use the kettle without fixing it.

2). Why do you use a measuring jug rather than the markings on the side of the kettle to measure the volume of water? The use of a measuring jug can allow for a more precise measurement. This will lower the error during the process. The markings on the side of the kettle might not be as accurate as well as those might just be a rough estimation. Measuring jugs are produced for this purpose and thus it should have a higher precision.

3). Why do you boil your kettle and then empty it before you start to record results? This is because at first, the whole kettle is at room temperature, including the heating elements and the wall of the kettle. If we directly use the first trial, the time should be significantly longer as the kettle has to first increase the temperature of the coil from room temperature to the normal temperature when it’s under load. Therefore, we have to do this procedure before we record the time for the first trial for better precision and consistency.

4).

5). How accurate is your measured value for cw? From the data sheet: 4186 J/kg o C My result: (3996 ± 445.5) J/kg o C As the theoretical value of the specific heat capacity of water lies within the boundary of my result, I think my measured value is decently accurate.

6). What could you do to get a more accurate result? Weighing the amount of water as well as using a measuring cup should increase the precision of the amount of water used in the trials. Using a thermometer can also increase the precision of the initial temperature of the water. Repeat the trials so that human errors can be minimized. Using a hair dryer to dry off the water inside the kettle after each trial might be beneficial to the precision of the investigation. We should also keep the down time between trials the same as this might affect the initial temperature of the whole kettle as well as the heating elements. We should also measure the final water temperature as the water might not be boiling even when the kettle stops.

Conclusion: I have successfully found out the specific heat capacity of water in this investigation and it’s pretty close [(3996 ± 445.5) J/kg o C] to the theoretical value (4186 J/kg o C). I would say this is a successful investigation....