Chapter 2; Lesson 2.1 T.O.C: Charge Needs a Continuous Path to Flow

Electric Charge Flows in a Loop *Remember* Electric current is electric charge that flows from one place to another Charge does NOT flow continuously through material unless the material forms a closed path, or loop. Circuit(w.w)- closed path thru which a continuous charge can flow. –Path provided by low-resistant material (usually wire) –Designed for specific jobs (like light a bulb)

Parts of a Circuit Typically have: 1.Voltage Source- Battery or power plant 2.Conductor- forms connection from voltage source to electrical device & back (usually wire) 3.Switch- designed to break the closed path of charge. When switch is open, it produces a gap so the charge cannot flow. 4.Electrical Device- any part of circuit that changes electrical energy in another form of energy. –Resistor(w.w)- electrical device that slows flow of charge in a circuit. This allows energy to be converted into light or heat. Ex: light bulb is a resistor. Converts energy into light.

Identify Circuit Parts

Open & Closed Circuits Current in circuit is similar to water flowing thru hose. However, if you cut hose in half the water keeps flowing out. Not so if you cut a wire in half. Most cords on appliances have 2 wires. One leads to device from source, the other goes from device back to source to complete the circuit. Switches work by opening/closing the circuit. Most circuits have standard symbols used to represent parts of a circuit. Paperclip/nails/switch Lab!

Current Follows the Path of Least Resistance Although current follows a closed path, the path does not have to be made of wire. All materials w/ low resistance are good conductors. This includes you. –This is why you should never use electronics w/ bare wires! –Water is a good conductor, especially when mixed w/ salt from a person’s skin. This is why you don’t use electronics near sinks/tubs full of water!

Dangers in Electricity Short Circuit Short circuit(w.w)- an unintended path connecting one part of a circuit with another. The current follows a path a closed path, but not the right one. 1.Functioning circuit- charge flows thru one wire to device and back thru other wire to outlet. 2.Short circuit- cord is damaged& 2 wires inside have formed a connection. w/out resistance from lamp there more current in the wire. This causes wires to overheat & start a fire. *Create Illustration Grounding Circuits Recall; when lightning strikes a rod, charge flows thru the least resistant path. This is why it hits the lightning rod instead of a house or person. The 3 rd prong (the ground) on some plug-ins acts in a similar fashion as the lightning rod. A circuit that connects stray current safely to the ground is a grounded circuit. Charge usually flow thru 1 prong to device & back thru 2 nd prong to outlet. If there is a short circuit; charge might flow dangerously to the outside of the shell of the appliance. If there is a ground wire; the current will flow along 3 rd wire & safely into ground, along buried rod or cold water pipe.

Imagine: you are sitting at home in the living room. The circuit for the room is currently supplying charge to your t.v. & several lights. You turn the A/C on & suddenly the circuit wires are providing more current than before. The lights dim. What has happened?

Safety Devices Control Current Imagine: you are sitting at home in the living room. The circuit for the room is currently supplying charge to your t.v. & several lights. You turn the A/C on & suddenly the circuit wires are providing more current than before. The lights dim. What has happened? Too much current is dangerous! There are safety devices built into circuits to prevent dangerous situations from occurring.

How Fuses Work Fuses automatically shut off current before circuits overheat. Fuses open circuits when there is too much current flowing thru. Found in cars, some appliances, and older houses Consist of thin strip of metal inserted into the circuit. The charge then also flows thru the fuse. Too much charge melts the metal strip causing the circuit to open. Fuses are measured in amps, because fuses monitor electric current. Build your own Fuse Lab!

Other Safety Devices Most modern homes use Circuit Breakers. (breaker boxes) They do not have to be replaced every time they open a circuit like fuses. How they work: when too much current is moving thru the circuit; a piece of wire in the breaker begins to heat up & expand which presses against a switch which flips off & opens the circuit stopping the flow of charge. Ground Fault Control Interrupter (GFCI)- Sometimes a little current leaks out of an outlet or an appliance. Often it is so small you don’t notice it. However, if you have wet hands, even a small amount of current is dangerous. GFCI- has tiny circuit inside which monitors incoming & outgoing current. If it detects a change in the current it will flip a switch to open the circuit Push the Reset button to close the circuit again.

Circuit Breaker

Ground-Fault Circuit Interrupter

2.1 Review Q’s 16 points 1.Describe the 4 parts of a circuit & explain what each one does. (8 pts) 2.Explain why short circuits are dangerous. (2 pts) 3.What is the purpose of a ground wire? (2 pts) 4.How do switches control the flow of electric current? (2 pts) 5.What do fuses & circuit breakers have in common? (2 pts)