Slide 1

ElectricityWhat comes to mind when you hear the word Electricity?Water boyLightningTeam workAc/Dc ChargeElectricity in our lives.Two different types current:Alternating current (AC): i.e. Outlets in walls

Direct Current (DC): i.e. Batteries, out the positive, in the negative.

Ohms LawOhms Law: the current between two points is directly proportional to thepotential differenceorvoltage, and inversely proportional to theresistance.V = IRV = Voltage/ Potential difference -Volt (V)I = Current Amp (A)R = Resistance Ohm ()

Voltage/Potential Difference.the electric potential difference is the difference in electric potential (V) between the final and the initial location when work is done upon a charge to change its potential energy. Refer to page 691 in text book.Think of gravitational potential difference.E = mgh

V = E/QV = Voltage/ Potential difference -Volt (V)E = change in electrical potential energy- Joule (J)Q = quantity of charge Coulomb (C)

Voltage/Potential Difference cont.Ex. A battery has a potential difference of 18.0 V. How much work is done when a charge of 64.0 C moves from the anode to the cathode? V= 18.0 VQ = 64.0C V = E/QE = VQE = (18.0V)(64.0C)E = 1152JCurrentCurrent: a flow ofelectric charge. From positive to negative.The currentcan be calculated with the following equation: I = Q/tQ = quantity of charge transferred Coulombs (C)t = time interval that the charge is transferred Seconds (s)Example 1: A toaster runs for 2.5 minutes in which 9.60 A of current were required. Find the amount of charge that passed through the toaster.I = 9.60 At = 2.5min = 150sI = Q/tQ = I tQ = (9.60A) (150s)Q = 1440 C

Current cont.ResistanceResistance: is the hindrance to the flow of charge.3 main variables that contribute to resistance.the total length of the wires will affect the amount of resistance. Longer the wire, more resistance.the wider the wire, the less resistance that there will be to the flow of electric chargethe material that a wire is made ofResistance cont.The conducting ability of a material is often indicated by its resistivity. Lower the resistivity the better the conductor.Kitchen appliances such as electric mixers and light dimmer switches operate by altering the current at the load by increasing or decreasing the resistance of the circuit.Example 2. A 30 V battery maintains current through a 10 resistance. What is the current?V = 30VR = 10V = IRI = V/RI = 30V/10I = 3.0A

Resistance cont.Ohm's Law as a Predictor of CurrentThe Ohm's law equation can be rearranged and expressed as: I = V/RThe current in a circuit is directly proportional to the electric potential difference.(battery voltage)The current is inversely proportional to the total resistance offered by the circuit.

Ohms Law as a predictor of current cont.With the formula: I = V/RBattery Voltage Total Resistance Current1.5V 3 0.5A3.0V 3 1.0A3.0V 6 0.5A3.0V 12 0.25APowerPower: is the rate at which electrical energy is supplied to or consumed by a circuit. P = E/tP = rate of change in potential energy Watt (W) E = change in electrical potential energy- Joule (J)t = time interval that the change occurs over Seconds (s)Power in Circuits. To determine the power across a circuit, we must combine the following 3 equations.P = E/tV = E/QI = Q/tP = (V)(Q)/tP = (V)(I) Power in Circuits cont.Ex. Determine the power of a saw that draws 12 amps of current when plugged into a 120V outlet.I = 12AV = 120VP = VIP = (120V)(12A)P = 1440W

Other formulas for calculating power:P = I2 R P =V2/ RHomework:Pg. 692 # 1, 2, 3Pg. 696 # 4, 5, 6Pg. 714 # 21, 22