Chapter 6 & 7: Electricity

Electricity The flow of electric current. The flow of electric energy carried by electrons.

Electric Circuits something that provides a path through which electricity travels Made up of wires, switches, resistors, capacitors, etc.

Open/Closed Circuits Open Circuit: a circuit in which there is a break in the wire so that current cannot flow,; a switch turned to the "off" position is one way to cause the break in the wire Closed Circuit: a circuit in which the switch is turned to the "on" position, causing there to be no breaks anywhere in the wire

Short Circuit Is usually an accidental extra path for current to flow. Can cause excess electrical energy to flow through parts of the circuit causing overheating of wires.

Electrical Charge Positive Charge-associated with protons. Negative Charge- associated with electrons. Like charges repel. Opposite charges attract. Amount of charge is measured in coulombs.

Static Electricity Build up of electrical charges on an insulator. Electrical charge doesn’t move.

Voltage The amount of potential energy that each unit of electrical charge has. The amount of push behind the electrical energy. Measured in volts using a voltmeter

Current Is the flow of electric charges. Measured in amperes (amps for short) using an ammeter. –Coulombs per second

AC/DC Alternating Current- current in which the direction changes back and forth. Direct Current- current flows in only one direction.

Resistance Electrical Conductor: materials which the charge flows very easily Electrical Insulator: materials which block the flow of electricity.

Resistance of Wires Larger diameter wires have less resistance than thinner wires. –A smaller gauge wire is thicker than a larger gauge wire. Shorter wires have less resistance than longer wires.

Ohm’s Law For a given voltage, the amount of current in a wire is inversely proportional to the resistance. V = I * R Not all materials obey Ohm’s law –Diodes are examples of electrical components that do NOT obey Ohm’s law.

Electrical Power P = V * I –substituting I*R for V, –P = I 2 * R

Electrical Safety Fuses, circuit breakers, & GFI outlets are used to prevent excessive amounts of current flowing through a circuit. This will prevent wires from overheating and causing a fire. Check the rating on extension cords before using them.

Series Circuit The current can only take one path. –I T = I 1 = I 2 = I 3 … The total voltage drop across the circuit is the sum of all the changes in voltage. –V T = V 1 + V 2 + V 3 … The equivalent resistor replacing all the resistors is the sum of the total resistance. –R T = R 1 + R 2 + R 3 …

Parallel Circuit The current has multiple paths. –I T = I 1 + I 2 + I 3 … The voltage drop across the circuit is the same across each branch. –V T = V 1 = V 2 = V 3 … The equivalent resistor replacing all the resistors is the sum of the total resistance. – 1 / R T = 1 / R / R / R 3 …