1. Power

2. An electrical circuit is a tool to transfer energy, energy is delivered by the circuit to the load.
Power is the rate at which electrical energy is supplied to a circuit or consumed by a load.

3. The symbol for power is P and the units are watts (W).
For this calculation time must be measured in seconds.
Power = Energy = E = P
Time t

4. Example A
If you have a circuit with a 750J battery and a current over 3 minutes?
3min x 60 s = 180s
P = E / t = 750J / 180s
= 4.17 W

5. Example B
How long would a 100 watt bulb last if you had 1500J of energy?
t = E/P = 1500J / 100W
= 16 seconds

6. Practice Problems
How many watts is a bulb if it uses 9000J in a minute?
P=E / t = 9000J / 60s
= 150 W

7. 2. If a 1605J battery is used over 5
2. If a 1605J battery is used over 5.0 minutes, what is the power produced?
5.0 min x 60s
= 300s
P=E / t = 1605J / 300s
= 5.35 W

8. 3. How long would it take a 100watt bulb to use 2500J?
t = E / P = 2500J / 100 W
= 25 seconds

9. 4. In one house how many joules is used by a 50watt bulb?
E = t x P = 3600 s x 50 W
= 180,000J

10. 5. If a battery produces 1 million joules, in an house how many watts will it produce?
J / 3600s
= 278watts