Table 1: Time taken to boil five different volumes of water Volume (L) Time 1 (s) Time 2 (s) Time 3 (s) Average uncertainty time (s) in the average time (s) 0. 25 57 57. 5 58 57. 5 0. 5 0. 5 95 94 96 95 1 0. 75 132 135 134 133. 7 1 1 169 171 168 169. 3 1. 5 1. 25 209 211 212 210. 7 1. 5 To keep the data more accurate, I empty and cooling the kettle thoroughly before doing the next boiling. Diagram 1 Average Time taken to boil water 250 y = 152. 28x + 19. 03 Time (s) 200 150 100 50 0 0 0. 2 0. 4 0. 6 0. 8 1 1. 2 1. 4 Volume (L)
As shown on the graph, there is a positive relation between time taken to boil water and the volume of water. The equation for this line is y = 152. 28x + 19. 03. Therefore, the gradient of this line is 152. 28. As initial and final temperature are set at 25. 0o C and 100o C and the power of the kettle is 2025w (middle of the power range 1850w-2200w). Therefore, the heat of water can be calculated by using the equation: gradient = ??????? ?? Where gradient is 152. 28, cw = the heat of water, ? T= change in temperature, P= power of the kettle. Therefore, cw =??????????????????? ?T = 152. 28? 2025?? 100o C? 25. 0o C = 308367 75 = 4111. 56J/kg ° C, which means it costs 4111. 56J of energy to rise 1kg of water by 1° C Question 1 The reason why boiling water by using an electric kettle without elements are completely underwater is dangerous is that with water level above the element the maximum temperature will reach is 100o C. Otherwise, elements in the kettle will be overheated and burnt down as a result. Since the kettle transfers electrical energy to heat. Or more seriously, the whole circuit might be broken.
Question 2 Different kettles may have different shapes and therefore the volume may not be set at a standard level. Instead, measuring jugs are produced under a standard level. Therefore, it would be more accurate to measure a specific volume of water. And as a result, time consumed to boil water would be more accurate with other elements are constant. Question 3 The reason why boil and empty the kettle before recording results is in order to make the kettle as empty as possible and cool the kettle down to the room temperature.
Question 5 Cw (Specific heat of water) is the amount of heat per unit of mass needed to raise the temperature by one degree Celsius. Since the Cw that I calculated is 4111. 56J/kg ° C which is close to the standard Cw which is 4200 J/kg ° the Cw I measured was quite C, accurate. Question 6 In order to get a more accurate result, some measuring methods could be improved. For example, fill water at a completely accurate level, precise timing and cool the kettle down to the room temperature after each use of it.