Electricity
5 marks · Normal2. An electric heater with resistance 46 Ω is connected in series with an ammeter and a 230 V mains supply.
Calculate the current through the heater.
State the SI unit for resistance.
Calculate the energy transferred by the heater in 30 seconds.
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) 5.0 A · must show V=IR rearranged to I=V/R, substitute values, 230/46=5A
(b) ohm; symbol Ω · must show ohm or Ω
(c) 34500 J · must show E=IVt, I=5A, V=230V, t=30s, E=5*230*30=34500J
Common mistakes: Using power formula incorrectly; Not using correct units for resistance or energy
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Uses I = V/R with values substituted.
A1 (a) · 1 mark · Correct calculation: 5.0 A (accept 5/rounded). (follow-through)
B1 (b) · 1 mark · States 'ohm' or symbol 'Ω'.
M2 (c) · 1 mark · Uses E = I × V × t with their own I. (follow-through)
A2 (c) · 1 mark · Final answer: 34500 J or follow-through using their current. (follow-through)
Worked solution
a. Use Ohm's law: I = V / R = 230 V / 46 Ω = 5.0 A.
b. The SI unit for resistance is the ohm (Ω).
c. Use the energy formula: E = I × V × t = 5.0 × 230 × 30 = 34500 J.