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
   • 12.5 A
   • 15 A, the size of the breaker
   • 180,000 A, from 1,500 × 120
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?

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

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

   • 3.0 kWh
   • 300 Wh, which is 0.30 kWh
   • 12 Wh, from 60 ÷ 5.0
   • 0.30 kW, a power unit for an energy
7. 7.

   A home uses 450 kWh in a month. How many joules is that, with 1 kWh = 3.6 × 10⁶ J, Noah?

   • 1.62 × 10⁹ J
   • 1.62 × 10⁶ J
   • 1.62 × 10¹² J
   • 1.25 × 10⁻⁴ J, from 450 ÷ (3.6 × 10⁶)
8. 8.

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

   • 0.8 kW, from 720 ÷ 900
   • 1.25 kW
   • 30 kW, from 900 ÷ 30
   • 27,000 kW, from 900 × 30
9. 9.

   Tala compares a 1,500 W heater run 4 h a day with a 150 W computer run 8 h a day, for 30 days. Which uses more energy?

   • They use the same, since both are plugged in
   • The heater: 6,000 kWh, from 1,500 × 4
   • The heater: 180 kWh, against 36 kWh
   • The computer, since it runs longer each day
10. 10.

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

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