1. Electric Power
Unit 12.3

2. Energy Transfer
When a battery is used to maintain an electric current in a conductor, chemical energy stored in battery is continuously converted to the electrical energy of the charge carriers.

3. Energy Transfer
As the charge carriers move through the conductor, this electrical energy is converted to internal energy due to collisions between the charge carriers and other particles in the conductor.

4. Energy Transfer
Electric power, then, is the rate at which charge carriers do work. Put another way, electric power is the rate at which charge carriers convert electrical potential energy to nonelectrical forms of energy.

5. Energy Transfer
Potential difference is defined as the change in potential energy per unit of charge: ΔV = ΔPE q

6. Energy Transfer
We can express electric power as current multiplied by potential difference: P = IΔV Power = current x potential difference

7. Energy Transfer
This equation describes the rate at which carriers lose electrical potential energy. In other words, power is the rate of conversion of electrical energy.

8. Energy Transfer
We learned that the SI Unit of power is the watt, W. In terms of the dissipation of electrical energy, 1W = 1J/s.

9. Energy Transfer
Most light bulbs are labeled with their power ratings. The amount of heat and light given off by a bulb is related to the power rating (wattage).

10. Energy Transfer
The conversion of electrical energy to internal energy in a resistant material is called joule heating.

11. Energy Transfer
Power companies charge for energy, not power. However, the unit of energy used by electric companies calculate consumption, the kilowatt-hour is defined in the terms of power.

12. Energy Transfer
The following equation shows the relationship between the kilowatt- hour and the SI Unit of energy is the joule: 1kW-h x 103W x 60min x 60s = 1 kW 1 hr 1min 3.6 x 106W*s or 3.6 x 106J

13. Energy Transfer
The electrical energy supplied by power companies is used to generate currents, which in turn are used to operate household appliances. This can be done by decreasing either current or resistance.

14. Energy Transfer
When transporting electrical energy by power lines, power companies want to minimize the loss and maximize the energy delivered to a consumer.

15. Energy Transfer
Although wires have little resistance, recall that resistance is proportional to length. So resistance becomes a factor when power is transported over long distances.

16. Energy Transfer
Even though power lines are designed to minimize resistance, some energy is lost due to the length of the power lines.

17. Energy Transfer
Thus transferring electrical energy at low currents, thereby minimizing the loss, requires that electrical energy be transported at very high potential differences.

18. Energy Transfer
Power plants transport electrical energy at potential differences up to 765,000V. This is reduced by a transformer in your town to about 4000V.

19. Energy Transfer
At your home, this potential difference is further reduced to about 120V by the transformer.