Electric power and the energy a home uses

Answer Key - Grade 11 Science Worksheet - Building Confidence

Circle the best answer, or write your answer on the line.

1. 1.

   Ari checks a heater element: 120 V across a 24 Ω resistance. How many watts does it use?

   600 W
2. 2.

   Bo checks a toaster element: 120 V across a 9.6 Ω resistance. How many watts does it use?

   1500 W
3. 3.

   Esme checks a small car heater: 12 V across a 1.2 Ω resistance. How many watts does it use?

   120 W
4. 4.

   A hair dryer label reads 120 V and 1,500 W. What current does it draw from a 120 V outlet, Jun?

   • 0.08 A, from 120 ÷ 1,500
   • 180,000 A, from 1,500 × 120
   • 15 A, the size of the breaker
   • 12.5 A
5. 5.

   A circuit has a 15 A breaker at 120 V. What is the most power it can supply before the breaker trips, Kira?

   • 18,000 W
   • 8 W, from 120 ÷ 15
   • 1,800 W
   • 135 W, from 120 + 15
6. 6.

   Luz compares a 1.0 kW microwave with a 1,200 W toaster. Which has the greater power?

   • The microwave, since a kilowatt is bigger than a watt
   • They are equal, since both labels give power
   • The microwave, since 1.0 kW is 10,000 W
   • The toaster: 1.0 kW is only 1,000 W
7. 7.

   Milo runs a 60 W bulb for 5.0 h. How much energy does it use?

   • 0.30 kW, a power unit for an energy
   • 300 Wh, which is 0.30 kWh
   • 3.0 kWh
   • 12 Wh, from 60 ÷ 5.0
8. 8.

   Pia compares a 100 W bulb on for 1.0 h with a 1,000 W heater on for 0.10 h. Which uses more energy?

   • The heater: 1,000 Wh against 100 Wh
   • Neither: both use 100 Wh
   • The bulb, since it runs ten times longer
   • The heater, since its power is ten times larger
9. 9.

   A home uses 900 kWh in a 30-day month. What is its average power, Ren?

   • 30 kW, from 900 ÷ 30
   • 0.8 kW, from 720 ÷ 900
   • 27,000 kW, from 900 × 30
   • 1.25 kW
10. 10.

    Zee runs a 1.5 kW oven for 40 minutes. How much energy does it use?

    • 60 kWh, from 1.5 × 40
    • 0.04 kWh, from 1.5 ÷ 40
    • 1.0 kWh
    • 1.5 kWh, the power as the energy