Name:______Date:______Hour: 1 2 3 4 5 6

Practice – Ohm’s Law and Electrical Power

Directions: show all work (GUESS method) on a separate sheet of paper. Don’t forget to write formulas, not triangles for equations. Answers are in bold so you can check your work. Assume 120 volts for anything plugged into a wall.

1) What voltage is required to make 0.25 A flow against 8 Ω of resistance? 2 v

2) What current flows in a circuit with a potential difference of 12v and a resistance of 25 Ω? 0.48 A

3) What is the resistance of a circuit with a voltage of 45v and a current of 5 A? 9 Ω

4) A circuit has 80 Ω of resistance. What voltage is required to push 25 mA through it? (convert mA to A) 2 v

5) A 40v circuit has a resistance of 80 Ω. How much current flows through it? How much power does the circuit use? a) 0.5 A, b) 20 W

6) 4 A flows through a circuit with a resistance of 8 Ω. What’s the potential difference across the circuit? How much power is in the circuit? a) 32 v, b) 128 W

7) How much current flows through the filament of a 75 W light bulb plugged in at home? 0.625 A

8) What is the resistance of a 600 W drill plugged into an outlet at home? 24 Ω

9) A walkman uses a standard 1.5v battery. How much resistance is in the circuit if it uses 0.01 A of current? 150 Ω

10) What current goes through a hair dryer plugged in at home if it has a resistance of 25 Ω? How much power does it use? a) 4.8 A, b) 576 W

11) How much current does a 12 v car battery push through a circuit with a resistance of 10 Ω? 1.2 A

12) How much current does a 900 W microwave use? How much resistance does it have? a) 7.5 A, b) 16 Ω

13) Your fuse panel at home has a 15 A circuit breaker. If more than 15 A try to flow in that circuit at one time, it will pop the breaker and shut down the circuit. You are cooking hot pockets in a microwave, and your mom turns on the vacuum cleaner. The microwave uses 1200 watts and the vacuum cleaner has 18 Ω of resistance. If the vacuum cleaner and microwave are turned on at the same time, will they pop the circuit breaker? What if it’s a 900 watt microwave? a) yes, b) no

14) A home stereo uses 120 volts to push 5.5 A to run properly. What is the resistance of the stereo? 21.8 Ω

15) If a kitchen appliance uses 3 A, how much power does it need? 360 W

16) What is the current in a microwave that requires 700 W of power? 5.83 A

17) What is the voltage in a circuit that uses 2640 W of power if 11 A of current flows in the circuit? 240 v

18) How much energy is used when a 120 kW appliance is used for 3 hours? (unit for energy is kW-hr) 360 kW-hrs

19) A TV has a power rating of 210 W. If it uses 1.68 kW-hrs of energy, how long has the TV been on? 8 hrs

20) How much does it cost to light six 100 W light bulbs for eight hours if the price of electricity is $0.09 per kilowatt hour? $0.054

21) An electric clothes dryer uses 4kW of electric power. How long did it take to dry the clothes if electric power costs $0.09 per kWh and the cost of running the machine was $0.27? 3 hrs

22) What is the resistance of a light bulb that draws 0.5 A of current? What is its power rating? a) 240 Ω, b) 60 W

23) How much current flows through a 100 W light bulb at home? 0.83 A

24) 8 amps of current flow through a hair dryer plugged in at home. How much electrical power does it use? 960 W

25) Compare the energy used by a 100 W light bulb for 10 hours and a 1200 W hair dryer used for 15 minutes? 1000 W/300 W

26) A toaster oven uses 10 A when plugged in at home. How much power does it use? 1200 W

27) A DVD player still uses 10 W of power even when not in use. What current still flows through it? 0.08 A

28) A potential of 25 v is applied to a circuit with a resistance of 25 Ω. How much current flows in the circuit? How much power is used? How much power would be used if the potential was 100 v? a) 1 A, b) 25 W, c) 100 W

29) A circuit with 47 Ω is connected to a 20 v battery. How much current flows in the circuit? How much power does the circuit use? a) 0.43 A, b) 8.51 W

30) A car power window draws 1.5 A when connected to a 12 v car battery. Calculate the resistance in the motor. Calculate the power used by the motor. a) 8 Ω, b) 18 W

31) How much current flows through a 1200 W toaster? How much resistance does it have? a) 10 A, b) 12 Ω

32) An RC car battery is 8.4 v and runs a 20 W motor. Calculate the current and resistance in the motor. 2.38 A, 3.53 Ω