1. Electric Circuits
Chapter 22 Section 3

2. Electric Circuits
If you connect a conductor (wire) between + and – terminals of battery, electrons flow in circuit
Amount of current determined by voltage of battery and resistance of conductor

3. voltage = current x resistance
Voltage & Resistance
As voltage increases, electric current in a circuit increases ( V , I )
As resistance increases, electric current in a circuit decreases (, I ↓)
Remember: Ohm’s Law
V = IR
voltage = current x resistance

4. Circuits
Control movement of electric current by providing paths for electrons to flow
Must provide an unbroken path for current to flow
Two kinds of basic circuits:
Series circuit
Parallel circuit

5. Series Circuit
Circuit that has only one path for electric current to follow
Path broken—current will no longer flow and all devices on circuit stop working
In series circuit, all electrical devices are connected along same current path
Current is same through each device

6. Each new device added to the circuit decreases the current
Each device has electrical resistance
Total resistance to flow of electrons increases as each additional device is added
By Ohm’s law, if voltage is constant, I  as 

7. Series Circuit

8. Broken Series Circuit

9. Parallel Circuits
Circuit that has more than one path for electric current to follow
Current branches so that electrons flow through each of the paths
If one path broken, electrons continue to flow through the other paths

10. Resistance in each branch can be different depending on the devices
The lower the resistance, the more current through the branch
Current in each branch of parallel circuit can be different

11. Parallel Circuit

12. Broken Parallel Circuit

13. Protecting Circuits
As current through the circuit increases, wires carrying current heat up
To keep wire from becoming too hot and causing fire, houses & buildings have circuit breakers that limit the
amount of current in the
wiring

14. When current becomes too large—a switch opens in the circuit breaker and stops the current
Once the cause of overload is removed, circuit can be used again by resetting the breaker

15. Cost of Electric Energy
Power—the rate at which energy is used
Amount of energy that is used per second
Amount of electric energy used depends on power of device and amount of time used

16. Charges customers for number of kWh used every month
Electric companies sell electric energy in units of kilowatt-hours, kWh
Equal to using 1 kW of power continuously for 1 hr
Charges customers for number of kWh used every month
Measured by an electric meter
(attached to home)

17. Electric Safety
1997—electric shocks killed an estimated 490 people in United States
Prevention is the key
Never use appliances with frayed cords
Unplug appliances before working on them
Avoid water when using plugged-in appliances
Never touch power lines with anything

18. Electric Shock Your body is like a piece of insulated wire
Fluids inside body are good conductors
Current can enter your body when you become part of an electric circuit
The effect of electric current on the body depends on the amount of current that flows into the body.