Alternating current and direct current
4 marks · NormalA lamp is connected to a 12 V battery and draws a current of 2.5 A. It is switched on for 4 minutes.
Calculate the power of the lamp.
Calculate the total energy transferred by the lamp in this time. Give your answer in joules.
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) 30 W
(b) 7200 J
Common mistakes: Using minutes instead of seconds for time
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Power calculated using .
M2 (b) · 1 mark · Convert 4 minutes to 240 seconds.
M3 (b) · 1 mark · Substitutes correct values into or . Allow FT from (a). (follow-through)
A1 (b) · 1 mark · Final answer for energy: 7200 J (accept answers to nearest 10 J). (follow-through)
Worked solution
(a) Power is given by .
(b) Time is 4 minutes = 4 60 = 240 s. .