A student investigated how the mass of water in an electric kettle affected the time taken for the water to reach boiling point - AQA - GCSE Physics Combined Science - Question 5 - 2019 - Paper 1

The starting temperature of the water should have been controlled to ensure consistency in the experiment.

The line does not go through the origin because there is a minimum mass of water needed for boiling; thus, even with zero water mass, there is a non-zero time for the kettle to switch off.

The results give a non-linear pattern because as the mass of water increases, the energy required to heat the water increases disproportionately due to factors such as increased heat loss to the surroundings.

First, we calculate the total energy transferred using the formula:

$E = P imes t = 2600 ext{ W} imes 120 ext{ s} = 312000 ext{ J}$

Then, using the equation for specific heat capacity:

$E = mc heta$

we rearrange to find the specific heat capacity, $c$:

$c = \frac{E}{m\Delta \theta} = \frac{312000 ext{ J}}{0.80 ext{ kg} \times (100 - 18)} = \frac{312000}{0.80 \times 82} = 4800 ext{ J/kg °C}$

Therefore, the specific heat capacity of water is approximately 4800 J/kg °C.