ELECTRICAL POWER
3 marks · NormalA mains-powered oven uses a heating element with a high resistance. The oven has a power rating of 2000 W and is switched on for 15 minutes.
State why the heating element must have a high resistance.
Calculate the total energy transferred to the oven in this time.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) So that it heats up and transfers energy to cook food. · must show mention heating up OR energy transfer to heat
(b) 1,800,000 J · must show correct use of E = P × t, conversion of time
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Explain that high resistance is needed for heating (energy transfer to heat).
M1 (b) · 1 mark · Correct formula and substitution for energy = power × time, using seconds.
A1 (b) · 1 mark · Calculates and states correct energy value with unit. (follow-through)
Worked solution
a) The heating element must have a high resistance so that it heats up as current passes through and cooks the food.
b) Power, P = 2000 W; Time, t = 15 min = 15 × 60 = 900 s. E = P × t = 2000 × 900 = 1,800,000 J.