ELECTRICAL POWER
4 marks · NormalA washing machine has a power rating of 1800 W. It is used for 40 minutes during a wash cycle.
Calculate the total energy transferred by the washing machine in one wash cycle.
Suggest one effect on the wash cycle if the heating element had a much lower resistance than normal.
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(a) 4,320,000 J · must show correct conversion of minutes to seconds; E = P × t
(b) A lower resistance would mean less heating, so the water would not get hot enough and washing would be less effective. · must show explain lower resistance = less heating, state effect on washing (less effective/longer wash)
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Marking points
M1 (a) · 1 mark · Correct formula and conversion of units (40 min to 2400 s).
A1 (a) · 1 mark · Calculates and states: E = 1800 × 2400 = 4,320,000 J. (follow-through)
M2 (b) · 1 mark · Explain that lower resistance results in less (or slower) heating.
A2 (b) · 1 mark · State that wash cycle would be less effective or take longer since water does not get hot enough.
Worked solution
a) Time = 40 min = 40 × 60 = 2400 seconds. E = 1800 × 2400 = 4,320,000 J.
b) A lower resistance heating element would not get hot enough—so the water in the washing machine would not reach the right temperature. Clothes would be less clean or need longer to wash.