Electric Circuits Chapter 22 Section 3

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

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

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

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

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 

Series Circuit

Broken Series Circuit

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

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

Parallel Circuit

Broken Parallel Circuit

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

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

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

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)

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

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.