A student heated water in an electric kettle - AQA - GCSE Physics - Question 7 - 2020 - Paper 1

The correct symbol for a thermistor is the one that looks like a rectangle with a line inside it. (Please refer to the image for clarity.)

Using the formula for power:

$P = I^2 imes R$ Where:

• I (current) = 12 A
• R (resistance) = 15 Ω

Calculating gives:

$P = 12^2 imes 15 = 144 imes 15 = 2160 ext{ W}$

The correct reason is that the heating element in the kettle takes time to heat up.

To obtain the results shown in Figure 10, the student could:

• Measure the mass of water using a balance or measure the volume using a measuring cylinder.
• Record the initial temperature of the water.
• Pour the measured water into the kettle.
• Place a thermometer in the water to monitor the temperature.
• Switch the kettle on and begin timing.
• Record the temperature at regular intervals, e.g., every 5 seconds.

To calculate the energy transferred: Using the specific heat formula:

$E = mcΔT$ Where:

• m (mass of water) = 0.50 kg
• c (specific heat capacity of water) = 4200 J/kg°C
• ΔT (temperature change) = 100°C - 20°C = 80°C

Calculating gives:

$E = 0.50 imes 4200 imes 80 = 168000 ext{ J}$

Calculate the energy transferred using the formula for latent heat:

$E = mL$ Where:

• m (mass converted to steam) = 5.0 g = 0.005 kg
• L (latent heat of vaporisation) = 226000 J/kg

Calculating gives:

$E = 0.005 imes 226000 = 1130 ext{ J}$