8 ELECTRICAL CONDUCTORS Conductors allow electrons to flowConductivity depends upon how tightly the atom holds on to its electrons.loose electrons in a material conduct the electric charge through (metals).Examples of conductors: Metal, graphite, etc.
9 ELECTRICAL CONDUCTORS In solid conductors, the electrons carry the charge through the circuit because they are loosely held. In fluids, like those in a car battery, positive and negative ions and electrons may compose the flow of electric charge.
10 ELECTRICAL INSULATORS Insulators DO NOT conduct electricity well!! They provide RESISTANCE to the flow of electrons.RESISTANCE IS CAUSED BY INTERNAL FRICTIONExamples of Insulators: Glass, wood, rubber, etc.
11 SEMICONDUCTORSSemiconductor – material made to behave sometimes as insulators and sometimes as conductors (germanium and silicon).
12 Electric FieldsAn electric field surrounds every electric charge and exerts the force that causes other electric charges to be repelled or attracted.Electric fields are represented by arrows that show how the electric field would make a positive charge move.
13 Charges Exert Forces Charges Exert Forces Unlike charges attract each other (positive and negative)Like charges repel each other (positive to positive or negative to negative)
14 Charges Exert ForcesJust like gravity, the amount of electrical force exerted on an object is related to the following:Distance from the charged objectStrength of the charge on the charged object
15 How can objects become charged? 1) Charging by Contact –Two objects are rubbed against each other and electrons are transferred.PROTONS NEVER MOVE from one atom to another.
16 How can objects become charged? OR, A charged object touches a neutral object, transferring electrons –PROTONS NEVER MOVE from one atom to another
17 How can objects become charged? Charging by Induction (charging at a distance) – A charged object is held near a neutral object and causes an overall charge.
18 Charge PolarizationWhen charges rearrange in an atom, one side becomes slightly more positive and the other side becomes slightly more negative. The atom is electrically polarized. Ex – charged comb attracting bits of paper or charged balloon sticking to the wall.
20 What is current electricity? Current Electricity - Flow of electronsWhat causes electrons to flow?When an electric force is applied, it causes a potential difference or difference in voltage between the ends of a conductor.When there is no potential difference, the flow of charge stops.
21 Direct Current and Alternating Current Direct Current – flow of charge always flows in one direction. Batteries use DC to flow from the negative terminal to the positive terminal.Alternating Current – electrons move back and forth about relatively fixed positions. Power utilities use AC. AC allows low-cost, high voltage energy transmission across great distances, with safe low-voltage use by the consumer.
22 Voltage DifferencePotential difference or voltage difference causes electrons to flow in one net direction. This voltage difference provides the “push” or the “pressure” to move in a given direction, and the SI unit is Voltage (volts)
23 Voltage SourcesVoltage sources: dry cell batteries, wet cell batteries, lead- acid batteries and generators.They supply the energy or the “push” to allow the charges to move.
24 Voltage Sources Dry Cell Batteries Consists of two electrodes surrounded by an electrolyte.In the dry cell shown here, one electrode is the carbon rod and the other is the zinc container.
25 Voltage Sources Wet Cell Batteries Contains two connected plates made of different metals in a conducting solution.
26 Voltage Sources Lead-Acid Batteries Most car batteries are lead-acid batteries.Contains six wet cells made of lead and lead dioxide plates in a sulfuric acid solution.
27 Voltage SourcesIn dry and wet cell batteries, a chemical reaction occurs releasing energy inside the cell which is then converted to electrical energy.Generators, like the alternators in vehicles, convert mechanical energy to electrical energy.
28 ResistanceResistance is the tendency of a material to oppose the flow of electrons, changing electrical energy into thermal energy and light.
29 Resistance Almost all materials have some electrical resistance. Conductors have less resistance than insulators.
39 SERIES AND PARALLEL CIRCUITS What is a series circuit?A series circuit has only one path for current.
40 SERIES AND PARALLEL CIRCUITS What is a parallel circuit?A parallel circuit has multiple paths for current.
41 SERIES AND PARALLEL CIRCUITS For a circuit to allow the flow of electrons, it must be closed which means that it makes a complete loop back to the power source.
42 SERIES AND PARALLEL CIRCUITS If it is open, the path that electrons can follow is broken and the resistor will not work.
43 SERIES AND PARALLEL CIRCUITS If there is a short circuit, the resistor will not work, even though there is a complete path.The reason is because electricity will always follow the path of least resistance and will therefore not travel through the resistor.
44 SCHEMATIC DIAGRAMSSchematic Diagrams are used to represent circuits.
46 FUSES AND CIRCUIT BREAKERS How do fuses work?Fuses melt to prevent circuit overloads.A fuse is a ribbon of wire with a low melting pointHow do circuit breakers work?Circuit breakers open circuits with high current.Made of a magnet or bimetallic strip