1. Aim: How can we explain electrical power and energy? Do Now: Which is brighter: 60 W light bulbs in series or 60 W light bulbs in parallel?

2. Electrical Power (P) The time rate at which electrical energy is usedThe time rate at which electrical energy is used Measured in Watts (W)Measured in Watts (W)

3. Formulas Ohm’s Law V = IR

4. Electrical Energy (W) The work done (or the energy expended)The work done (or the energy expended) Measured in JoulesMeasured in Joules

5. Substitute P = VI Substitute P = I 2 R

6. ResistorRΩVVoltsIAmpsPWatts 122100.764.58461.48 21777.864.58356.6 3941.224.58188.8 Total482204.581007.6 4751101.47161.3 53301100.3336.67 6501102.2242 Total27.51104440 Series Parallel Complete the Chart

7. Calculate the energy dissipated through resistor 2 in: 1 s W = Pt W = (356.6 W)(1 s) W = 356.6 J 1 minute W = Pt W = (356.6 W)(60 s) W = 21,396 J 1 hour W = Pt W = (356.6 W)(3,600 s) W = 1,283,760 J

8. Path of Least Resistance When given the opportunity, current will always take the path of least resistance Example: Students and homework

9. Kirchoff’s Laws 1. The current entering a junction must equal the current leaving a junction Junction Gustav Robert Kirchhoff 1824-1887

10. 5 A3 A 8 A 6 A2 A

11. 2. For any loop in a circuit, the sum of the voltage drops must be equal to the voltage gains.

12. 8 V 12 V 4 V 24 V Voltage Gains Voltage Drops V T = 24 V (battery) V 1 = 8 V V 2 = 12 V V 3 = 4 V = 24 V