1. Aim: How can we explain parallel circuits? Do Now: A series circuit has 3 resistors, 20 Ω, 40 Ω, and 60 Ω. What is the total resistance? R T = R 1 + R 2 + R 3 R T = 20 Ω + 40 Ω + 60 Ω R T = 120 Ω R T in series is always larger than the largest resistor!

2. Parallel Circuits A circuit with 2 or more current loops

3. Draw 2 resistors and a battery in a parallel circuit

4. Or…

6. Light Bulb Demo If one goes out, the others remain lit

7. In a parallel circuit… Voltage is constant Total current is the sum of the currents through each resistor

8. And resistance… Straw Demo R T in parallel is always smaller than the smallest resistor!

9. R 1 = 10Ω, R 2 = 20Ω, R 3 = 30Ω, in parallel with a V T = 100V Draw this circuit Calculate the current though each resistor R 1 = 10Ω R 2 = 20Ω R 3 = 30Ω V T = 100V

10. VIR 1100V10 A10Ω 2100V5 A20Ω 3100V3.3 A30Ω T100V18.3 A5.5 Ω

11. Draw a parallel circuit with a battery, 3 resistors, an ammeter reading the current through R 1 and an ammeter reading the current through R 3. R 1 = 2Ω, R 2 = 4Ω, R 3 = 8Ω, and the ammeter for R 3 reads 2.5 A. R 1 = 2Ω R 2 = 4Ω R 3 = 8Ω I 3 = 2.5A

12. VIR 120V10 A2Ω2Ω 220V5 A4Ω4Ω 320V2.5 A8Ω8Ω T20V17.5 A1.1 Ω