Power and Energy
1. If a blender is plugged into a 110 V outlet that supplies 2.7 A of current, what amount of power is used
by the blender?
2. What is the heat produced in a conductor in 25.0 s if there is a current of 11.0 A and a resistance of 7.20
Ω?
3. What is the current through a 400 W electric appliance when it is connected to a 120 V power line?
4. Tommy runs his juicer every morning. The juicer uses 90 W of Power and the current supplied is 4.5 A.
What is the internal resistance of the juicer?
5. If a clock expends 2 W of power from a 1.5 V battery, what amount of current is supplying the clock?
6. What is the resistance of a 150 W light bulb running on a 120 V circuit?
7. If the power company sells electrical energy at 11 cents/kWh, how much does it cost to run a 100 W
radio for 3.0 hours?
8. If the power company charges us 8 cents/kWh for electricity, what does it cost to operate the 1200 W
hair dryer for 15 minutes?
9. A certain coffeepot draws 6.0 A of current when it is operated on 120 V household lines. If electrical
energy costs 18 cents per kilowatt-hour, how much does it cost to operate the coffeepot for 4 hours?
10. A 2.0 A, 120 V electric motor that lifts a 6 kg mass against gravity at an average velocity of 0.4 m/s.
Determine the efficiency of the motor.
11. You asked to design a circuit to supply an electric motor with 0.6 A of current at 100 V potential
difference.
a. Determine the resistance in the circuit.
b. Determine the power to be supplied to the motor.
c. Determine the electrical energy to be supplied to the motor in 60 s.
d. Operating as designed above, the motor can lift a 10.0 kg mass a distance of 4.0 m in 10 s at
constant velocity. Determine the efficiency of the motor.