Electricity

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

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.

Coulomb’s Law where F is the force acting between two charges- q 1 & q 2 and d is the distance between them. k = 9.0 x 10 9 Nm 2 /C 2 1 C is 6.24 x electrons F = k q1q2q1q2 d2d2

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

Charged Objects Charged friction: creates an electrical charge on neutral object Conduction: a charged object loses some of its charge to an object by touching it. Induction: a charged object creates an induced charge on a neutral object simply due to its vicinity

Insulators & Conductors Insulator: materials in which electrons are highly attracted to the atom and requires much force to move them Conductor: substances in which electrons are weakly attracted to the atom and easily moves.

Grounding Touching a charged object with a conductor to dissipate the charge from the object. Lightning rod: a pointed rod that provides a source to constantly discharge electrical charge buildup in the air.

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.

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

Electric Fields Force field surrounding electric charges. magnitude determined by the effect on single “test charge” direction determined by direction of the force on a positive test charge (at the same point) Lines close together are strong Lines far apart are weaker -

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.

Voltage (Electric Potential) The amount of potential energy that each unit of electrical charge has. The amount of push behind the electrical energy. Measured in volts (J/C) using a voltmeter Voltage is often referred to as EMF- electromotive force.

Electric Potential Pictorial low voltage- the positive charge is not near the positively charged object high voltage- work was done to move the positive charge near the positively charged object

Current Is the flow of electric charges caused by a potential difference. 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. Measured in ohm (  ).

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. 14 gauge wire9 gauge wire

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

Electrical Power Power: energy used (work done) per second power is measured in watts. –watt = V * A = J/C * C/s = J/s P = V * I –substituting I*R for V, –P = I 2 * R

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 …