1. Power and Energy Energy Power
The ability to do work. Symbol: E Unit: Joule (J)
The amount of energy used in a given amount of time. Symbol: P Unit: Watt (W)

2. Electrical Power P = Power in Watts E = Energy in Joules
Δt = change in time in Seconds
One watt is equal to one joule per second.

3. Formulas E P t

4. Another Power Formula P = IV P I V
Power can also be expressed as a function of potential difference and current intensity.
P = IV P I V

5. Calculating Cost The cost in Quebec is approximately $0.08/kWh.
A kWh is a measure of energy.
P = Power in Kilowatts (kW)
t = time in hours (h)
E = Energy in Kilowatt hours (kWh)
How many Joules are in 1 kilowatt hour?

6. So which units do I use? P  Watts (W) t  Seconds (s) E = Joules (J)
P  Kilowatts (kW)
t  Hours (h)
E  Kilowatt hours (kWh)

7. Practice Problem A toaster uses 10 A of current on a 120 V line.
What is the power rating of the toaster?
How much energy does the toaster use if it takes 3.0 minutes to make toast?

8. What is the cost of operating this blender (500 watts) for 12minutes at a cost of $0.0827/kWh (taxes included)

9. The resistance of a lamp is 50Ω
The resistance of a lamp is 50Ω. The lamp is plugged into a 100V power supply. How much energy is used in 2.0 hours?
The resistance of an appliance is 2.0 Ω. 400kJ of energy is used at a current of 10A. How much time was the appliance plugged in?
J = 1.4x106 J
2000 seconds = 33min

10. Homework
Workbook Pages 79-82