Current Electricity Review
1. What amount of energy does a kettle use to boil water if it has 800 C of charge passing through it with a
potential difference of 120 V?
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2. What is the potential difference across a refrigerator if 75 C of charge transfers 9.0 x 10 J of energy to the
compressor motor?
3. An electric baseboard heater draws a current of 6.0 A and has a potential difference of 240 V. For how long
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must it remain on to use 2.2 x 10 J of electrical energy?
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4. A flash of lightning transfers 1.5 x 10 J of electrical energy through a potential difference of 5.0 x 10 V
between a cloud and the ground. Calculate the quantity of charge transferred in the lightning bolt.
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5. Calculate the energy stored in a 9.0 V battery that can deliver a continuous current of 5.0 mA for 2.0 x 10 s.
6. If a charge of 0.30 C moves from one point to another in a conductor and, in doing so, releases 5.4 J of
electrical energy, what is the potential difference between the two points?
7. How much charge is transferred by a current of 0.40 A in 15 min?
8. How long does it take for a current of 7.5 mA to transfer a charge of 15 C?
9. What is the potential difference between two points if 1 kJ of work is required to move 1 C of charge
between the two points?
10. What is the energy of an electron accelerated through a potential difference of 1.0 MV?
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11. What is the potential difference between two points when a charge of 80 C has 4.0 x 10 J of energy
supplied to it as it moves between the points?
12. There is a current of 0.50 A through an incandescent lamp for 2.0 min, with a potential difference of 120 V.
How much energy does the current transfer to the lamp?
13. There is a current of 2.0 A through a hair-blower that transfers 10,800 J of energy to the blower in 45 s.
What is the potential difference across the hair-blower?
14. An electric toaster operating at a potential difference of 120 V uses 34 200 J of energy during the 30 s it is
on. What is the current through the toaster?
15. An electric drill operates at a potential difference of 120 V and draws a current of 7.5 A. If it takes 50 s to drill
a hole in a piece of steel, calculate the amount of electrical energy used by the drill in that time.
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16. An electric motor is used to do the 9.6 x 10 J of work needed to lift a small load. If the motor draws a
current of 2.0 A for 20 s, calculate the potential difference across the motor.
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17. In a lightning discharge, 30 C of charge move through a potential difference of 108 V in 2.0 x 10 s.
Calculate:
(a) the current represented by the lightning bolt,
(b) the total energy released by the lightning bolt.
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18. Find the energy gained by an electron when it is accelerated through a potential difference of 3.0 x 10 V.
19. A 12 V automobile battery is rated by its manufacturer at 60 A·h. That is, it can deliver a current of 1.0 A
continuously for a period of 60 h, or 60 A for 1.0 h, or any other equivalent combination before needing to be
recharged. Calculate:
(a) how long the battery can deliver a current of 180 A.
(b) the total charge the battery is able to deliver without recharging,
(c) the total amount of electrical energy that is stored in the battery.
20. How much energy is required to dry your hair, if the hair dryer draws 12 A from a 110 V outlet for 6.0 min?
Answers
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1. 9.60 x 10 J
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2. 1.2 x 10 J
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3. 1.5 x 10 s
4. 30 C
5. 90 J
6.
7.
8.
9.
10.
18V
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3.6x10 C
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2.0 X 10 s
1kV
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1.6 x 10 J
11.
12.
13.
14.
15.
5.0V
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7.2 X 10 J
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1.2 X 10 V
9.5 A
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4.5 X 10 J
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16. 2.4 x 10 V
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17. (a) 1.5 x 10 A
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(b) 3.2 x 10 J
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18. 4.8 x 10 J
19. (a) 0.33 h
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(b) 2.2 x 10 C
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(c) 2.6 X 10 J
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20. 4.8 x 10 J