1. A battery raises the potential energy of a charge by an amount equal to qΔV. ΔV is the potential difference of the battery.

2. The chemical energy of the battery decreases by the same value: q ΔV
The chemical energy of the battery decreases by the same value: q ΔV. As the charge moves through the circuit the energy of the particle drops by the same value: q ΔV.

3. So a battery raises the potential energy of a charge and a circuit lowers the PE by the same amount. The voltage rise in a battery is equal to the voltage drop in the circuit.

4. In any circuit, the total of all voltage rises is equal to the total of all voltage drops. A voltage rise is an increase in PE per charge; a voltage drop is a decrease in PE per charge.

5. Power is work/time or ΔPE/time
Power is work/time or ΔPE/time. Electric power is calculated from this equation: P = I ΔV.

6. The SI unit of power is the watt, W. 1 W = 1 J/ 1 s.

7. P = IV and V = IR can be combined to form: P = I2R and P = V2/R.

8. An electric space heater is connected across a 120 V outlet
An electric space heater is connected across a 120 V outlet. It dissipates 1320 W of power. Calculate the resistance of the heater.

9. Electric companies charge by units of energy, but they do not use joules. The unit used is kilowatt•hours.

10. A kilowatt•hour is the energy delivered in 1 hr at a constant rate of 1 kW.

11. 1 kW•h = 3,600,000 J, or 3.6 X 106 J, or 3.6 MJ.

12. How much does it cost to operate a 100
How much does it cost to operate a W light bulb for 24 h if electrical energy costs $0.080 per kW•h?

13. Electrical wires have an energy loss calculated by P = I2R
Electrical wires have an energy loss calculated by P = I2R. This is called an I2R loss.

14. Electric companies want to decrease this I2R loss when delivering electricity. This can obviously be done by decreasing I or R.

15. Decreasing I is more effective since it is squared
Decreasing I is more effective since it is squared. P = IV so P stays the same if I is high and V is low or if I is low and V is high.

16. Since decreasing I is preferable due to I2R loss, electricity is transferred at high V and low I.

17. Power plants transport electricity at potential differences of up to 765,000 V.

18. A transformer reduces this voltage to about 4000 V
A transformer reduces this voltage to about 4000 V. At your home it is reduced by another transformer to about 120 V.