1. Electric Circuits A circuit is a path where a current can flow If the flow is to be continuous, the can be no gaps in the path Introduce gaps in the form of switches, so we can control completing a circuit Most circuits have more than one device that we want to provide with electrical energy

2. Electric Circuits There are two ways to connect multiple devices to a voltage source One is called series The other is called parallel Each has unique properties which we now examine

3. Series Circuits

4. A single pathway through the circuit The current is the same everywhere in the circuit Each device provides resistance and total resistance is the sum of the devices Voltage divides among the devices Voltage drop across each device is Ir device

5. Parallel Circuits

6. Each device connects to the voltage source Voltage is the same across each device Current from source divides into devices Total current is the sum of device currents Current in each device is just V/R Add devices, lower total resistance

7. Circuits Ignore resistance of wires for calculations Just as we ignored air resistance Ohm’s Law answers all questions Let’s do some sample calculations

8. Series Circuit Calculation 12 Volt 10 ohm20 ohm30 ohm

9. Parallel Circuit Calculation 12 Volt 10 ohm 20 ohm 30 ohm

10. Electric Power Moving charges do work We can heat the filament in a light bulb We can turn the rotor in a motor The rate at which work is done is power Electric Power = current x voltage Units are watts = joules/sec = amps x volts

11. Electric Power

12. Power Calculation 12 Volt 10 ohm20 ohm30 ohm

13. Power Calculation 12 Volt 10 ohm 20 ohm 30 ohm

14. Energy Loss in Power Lines Wires have some resistance To transport energy from Point A to Point B, we connect wires Each wire has resistance Energy Loss in one second is I 2 R Make I small to minimize Transformers convert AC Voltages

15. Fuses Limit the current that runs through wires in your house These wires have some resistance Energy loss by I 2 R converts to heat Hot wires can start a fire Limit the current with a fuse or circuit breaker