Chapter 7 Section 3

Circuits Circuits have: How many electrical devices can you see in this room?  Circuits have: 1)  source of voltage difference (battery or outlet) 2)  device that uses the energy (light) 3) conductors (wires) form a closed path to device

Series Circuit Example:  A string of Christmas lights, when one light burns out, no lights will work.  Why?  Because that burned out bulb breaks the circuit to all the bulbs.   Each bulb along the path shares the voltage, so the bulbs may appear dim.

Parallel Circuits Series circuits aren't a good way to wire a house.  If you turned off one light, then all the lights would go out.  Parallel circuits contain two or more branches Disadvantage:  Even when you turn a light off, current continues to flow through the system.    This is why you shouldn't stick a fork in an electric socket!

A switch can break a circuit And turn a device on or off Would this switch still work?

Identify the type of circuit: ______________________ ______________________

Symbols for writing a circuit

What is a fuse? Fuses contain a tiny piece of metal that melts if the current gets too high - this breaks the circuit. Too many appliances on in one room can overload the circuit and blow a fuse.

Where does electricity come from? Most electricity comes from converting heat energy into electrical energy - burning fossil fuels such as coal and natural gas. Some electricity is generated from dams, and nuclear reactors

How do dams generate electricity? As water flows through the dam it spins turbines, which will create electricity. These are referred to as: HYDROELECTRIC DAMS

Electricity by magnets Magnets have a magnetic field. This field can manipulate the flow of electrons which means it can produce electricity. By moving or turning a magnet you can force the flow of electrons.

Cost of Electricity 1)  Most companies charge by the amount of energy used 2)  This is measured in kilowatt hours (kWh) 3)  Each light bulb in your house costs money to leave on! 4)  Meters outside your house measure how much energy is used Check out: http://www.energyeducation.tx.gov/

What is the difference between alternating current and direct current? Check out   http://www.pbs.org/wgbh/amex/edison/sfeature/acdc.htmlhttp://www.pbs.org/wgbh/amex/edison/sfeature/acdc.html AC =  alternating current DC = direct current Direct Current is found in simple circuits like a battery powered flashlight.

Alternating Current   The direction of current flowing in a circuit is constantly being reversed back and forth. This is done with any type of AC current/voltage source. AC power is used in homes and business.  It's cheaper and easier to make devices for AC power, and you can easily increase and decrease the current.

1.  What happens when an object has an excess number of electrons? 2.  Name something that is a conductor: 3.  What unit is electric current measured in? 4.  What unit is electric energy measured in (think power bill)? 5.  The force that causes electrons to flow is the ____________ difference.

6. Is the image showing a parallel or series circuit? 7.  Where does the electricity come from that powers your house? 8.  What causes a fuse to be blown? 9.  _________ Law can be used to calculate voltage. 10.  Resistance is the tendency for  ____________ to oppose the flow of  ____________.