1. The Cost of Electricity

2. Power
We compare electrical devices by looking at how much power they use.
The symbol for Power is P
The unit for power is Watt (W)

3. a light bulb is 60 W a microwave is 1500 W a clothes dryer is 5000 W
For Example:
a light bulb is 60 W
a microwave is 1500 W
a clothes dryer is 5000 W

4. A larger unit for power is the kilowatt (kW) 1 kW = 1000 W
To convert Watts to Kilowatts divide by 1000.

6. Turn to the Science 9 Electricity – Study Questions Sheet
Complete question 1

7. Question 1
2000 W

8. b W

9. c W

10. d.1650 W

11. e. 500 W

12. f. 8 W

13. Turn to Science 9 Electricity – Study Questions Sheet
Cost
To find the cost of electricity, multiply the price by the power (in kW) by the time (in h).
Cost = Price x Power x Time
Turn to Science 9 Electricity – Study Questions Sheet

14. Question 2
A 6 kW heater runs for 3 hours. If electricity is sold at a rate of 5 cents/kWh, what is the cost of the electricity used?

15. Question 2 P = 6 kW t = 3 hours Price = 5 ¢/kW∙h
Cost = Price x Power x Time
= 5 ¢/kW∙h x 6 kW x 3h
= 90 ¢

16. Question 3
Calculate the cost of operating a 400 W spotlight for 2.0 h at a rate of 6.0 cents/kWh.

17. Question 3 P = 400 W t = 2 hours Price = 6 ¢/kW∙h
Cost = Price x Power x Time
= 6 ¢/kW∙h x 0.4 kW x 2h
= 4.8 ¢

18. Question 4
Find the cost of operating a 3600 W oven for 3.0 h, at a rate of 5.0 cents/kWh.

19. Question 4 P = 3600 W t = 3 hours Price = 5 ¢/kW∙h
Cost = Price x Power x Time
= 5 ¢/kW∙h x 3.6 kW x 3h
= 54 ¢

20. Complete Practice Questions on sheet provided
Classwork/Homework
Complete Practice Questions on sheet provided