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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 = I2 * 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. – IT = I1 = I2 = I3 … • The total voltage drop across the circuit is the sum of all the changes in voltage. – VT = V1 + V2 + V3 … • The equivalent resistor replacing all the resistors is the sum of the total resistance. – RT = R1 + R2 + R3 … Parallel Circuit • The current has multiple paths. – IT = I1 + I2 + I3 … • The voltage drop across the circuit is the same across each branch. – VT = V1 = V2 = V3 … • The equivalent resistor replacing all the resistors is the sum of the total resistance. – 1/RT = 1/R1 + 1/R2 + 1/R3 …