2 Positive and Negative Charges Protons = positive chargeElectrons = negative chargeMost atoms have the same number of protons and electrons and thus will have no net charge.Atoms become charged when they gain or lose electrons.
3 Static ElectricityThe accumulation of excess electric charges on an object
4 Electricity obeys rules??? Law of conservation of charges - Charges can be transferred from object to object, but cannot be created or destroyed.Opposite charges attract, like charges repel.electrons move easier through conductorsex. metalsElectrons do not move easy through insulatorsex. plastic, wood, rubber, and glass
5 Transferring Electric Charge Charging by contactprocess of transferring charge by touching or rubbingEx. Static electricity from rubbing your feet on carpetCharge by inductionthe rearrangement of electrons on a neutral object caused by a nearby charged objectEx. a negatively charged balloon near your sleeve causes an area of your sleeve to become positively charged
6 Transferring Electric Charge Static dischargeA transfer of charge through the air b/w two objects because of a buildup of static electricityEx. Lightning
7 Read Page 197 Write and Answer the following questions When the warm humid air rises to meet the cold air, what causes the air masses to churn together?What electric property causes the negative charges in the cloud to be attracted to the positive charges in the ground?Why does the ground below a cloud have a concentration of positive charges?
9 Electric currentThe flow of charges through a conductor (like a wire) is called electric current.Usually the flow of electronsMeasured in Amperes (A)Flow from high to low voltage.A voltage difference is the push that causes charges to move.Voltage difference is measured in volts (V).
10 CircuitFor charges to flow, the wire or conductor must always be connected in a closed path called a circuit.
11 Sources of Electricity Dry Cell BatteryWet Cell BatteryWall Socket
12 Sources of Electricity Dry cell battery - produces voltage difference b/w its zinc container and its carbon suspension rod, causing current to flow b/w themWet cell battery – contains two connected plates made of different metals in a conducting solution.Wall sockets – have a voltage difference across the two holes of an electrical outlet, and a generator at a power plant provides this voltage difference
13 ResistanceThe tendency for a material to oppose the flow of electrons, changing electrical energy into thermal energy and light.All materials have some electrical resistance.Measured in ohms (Ω)Making wires thinner, longer, or hotter increases the resistance.
14 Ohms Lawcurrent (in amperes) = voltage difference (in volts) resistance (in ohms) I = V/R
16 Ohms LawExample Problem #1: What is the current in a 30V circuit if the resistance is 6Ω? current (in amperes) = voltage difference (in volts) resistance (in ohms) I = ? V = 30V R = 6Ω
17 Ohms LawExample Problem #2: An Ipod uses a standard 3.7 V battery. How much resistance is in the circuit if it uses a current of A? current (in amperes) = voltage difference (in volts) resistance (in ohms) I = V/R
19 Series CircuitSeries circuit - The current only has one loop to flow throughParts of the circuit are wired one after another, so the amount of current is the same through every partEx. String of holiday lights
20 Parallel CircuitParallel circuit – contains two or more branches for current to move throughParts can be turned off without affecting the entire circuitEx. the electrical system in a house
21 Household Circuits Parallel circuits connected in a logical network. Electric energy enters your home at the circuit breaker or fuse box and branches out to wall sockets, lights, and major appliancesGuards against overheatingElectric fuseCircuit breaker
22 Electrical EnergyElectrical energy is easily converted to thermal, radiant or mechanical energy.Electrical power – the rate at which electrical energy is converted to another form of energyElectrical power is expressed in watts (W).Power = current X voltage differenceP(watts) = I (amperes) X V (volts)
23 Example ProblemYour microwave runs at a current of 10 amps. A standard plug in your house has a voltage difference of 120 volts. How much electrical power does it take to run this appliance?P = I x V
24 Example problem 2If it takes 1750 watts of power to run my hairdryer, and we know that it is plugged up to 120 volt outlet what must be the current?P = I x V