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Transcript
comes from the electrons in an atom when they are transfered them between objects. ++ electrons have a negative (-) charge 1 Static Current Build-up of electrical charge Electrons move in non-specific directions Flow of electricity through wires Examples – lightning, zap from carpet when touch something, static cling in clothes and hair Examples – anything with a cord or wire to power, hair dryer, phone, iPod Electrons move in definite paths 2 Most objects tend to be meaning that they have equal number of positive and negative charges. # of Protons = # of Electrons (positive charge) = (negative charge) = 3 Net Charge of Objects Charged Object Neutral Object -8 -6 +8 Net Charge: 0 +10 Net Charge: +4 4 Law of Electrical Charges Opposite Charges Attract + - Same Charges Repel + - - - + + + 5 Demonstration: How do Balloons stick to walls? + + - -+ - 1. Rub a balloon on a sweater to “charge it up.” 2. Negative charges in the wall repel from the balloon. - 3. The balloon sticks because the positive charges left over are attracted to the balloon. 6 A battery uses chemical energy to move electrical charges. 7 + Circuits flow in a circular path from positive end to negative end 8 + Light will not go on because the wire is not connected to the battery; no current will flow. 9 + Light bulb turns on because the electrical current can now flow through the complete circuit. 10 • an accidental path for current to flow • often causing risk of shock or fire • a branch with zero or very low resistance 11 Safety Devices Fuse - small piece of metal that melts if the current becomes too high opening switch Circuit breaker - piece of metal that bends when it gets over heated opening switch because current is too high GFI (ground fault interrupter) - usually found in bathrooms or garages shuts off plug when current if too high. 12 • Wire + • Power Source (1.5 V) • Bulb • Resistance open closed • Switch 13 Series Circuits Parallel Circuits WATCH! Do you notice any difference between the wirings of the two circuits above? 14 Series Circuits The light bulbs turn on. .75 V .75 V Battery is 1.5 V + However, since the voltage drops, the lights are dimmer. 15 Series Circuits If this light bulb does not turn on, Burned out light bulb This is because the circuit is broken here; Battery is 1.5 V neither light bulb will turn on. so the current can’t flow to this bulb here. + Christmas lights were commonly made this way. 16 Parallel Circuits Current divides and has more than one path. + 17 Parallel Circuits The current divides because it has more than one path. + Even though the path is stopped, the other light turns on because its circuit is not broken. Burned out light bulb Your house is wired with parallel circuits. Why do you think this is so? 18 … house was wired in series. What would happen if a light bulb burned out? How would you have to find out which one it was to fix? 19 Series Circuits Parallel Circuits Only 1 path for electricity to go Many paths for electricity to travel When 1 light in the path goes out, they all go out because there is no other path. When 1 light in the path goes out the electricity can find another way to transfer the current Voltage is reduce by each resistance added like another light bulb, heater, or appliance. Voltage is the same at each branch because each branch is like a separate series circuit connected to a source. Current is the same in all points Each branch does NOT always have the same current because it depends on how much resistance is in each branch. Example: Saw has more than a lamp 20