1. Electricity

2. Conservation of Charge  This attracting and repelling behavior is attributed to a property called charge.  Electrons and protons have electric charge.  In a neutral atom, there are as many electrons as protons, so there is no net charge.  The principle of conservation is that net electric charge is neither created nor destroyed, but is simply transferred from one material to another.

3. Charges cause Electrical Forces Electrical Forces: A force that one charge exerts on another. What is the charge on the following?  Electrons: Negative  Protons: Positive  Neutrons: Neutral (no charge)

4. Charges cause Electrical Forces When the charges are the same sign, they repel. Like charges repel. When the charges are opposite signs, they attract. Opposites attract.

5. Electric Fields  Just like the space around the earth is filled with a gravitational pull, the space around every electric charge is filled with an electric field. Electric Field: An aura than extends through space.  These vectors (magnitude and direction) are called electric field lines.  When the lines are farther apart, the field is weaker.  When the lines are closer together, the field is stronger.

7. Static Electricity and Charging Static electricity is the build up of charges on an object.  Charge can be transferred between objects.  The total charge in an isolated system is constant.

8. Ways Objects Acquire and Transfer Charge 1.Friction: rubbing two objects together  One object gains electrons and one object loses electrons Example:  Rubbing a balloon against your hair  Walking across the carpet

9. Ways Objects Acquire and Transfer Charge 2.Conduction: electrons flow through one object to another by contact Example:  Electrical wires

11. Ways Objects Acquire and Transfer Charge 3.Induction: electrons are rearranged in a neutral object when a charged object comes near Example:  Balloon stuck to a wall  Lightning

12. Ways Objects Acquire and Transfer Charge Static discharge is the loss of static electricity as electric charges move off an object.

13. Lightning rods are used to protect structures. The discharged electrons go into the ground!

14. Conductors and Insulators Whether a substance is classified as a conductor or an insulator depends on how tightly the atoms of the substance hold onto their electrons. Conductors: Outer electrons of the atom in a metal are not anchored to the nuclei of particular atoms, they are free to roam in the material.  Their electrons are loose– “sea of electrons”. Insulators: Electrons in other materials, rubber and glass for example, are tightly bound and remain with particular atoms.  Electrons are not free to wander.  These materials are poor conductors of heat and electricity.

15. Conductors and Insulators Semiconductors: Materials can be made to behave as an insulator and as a conductor. Superconductor: At temperatures near absolute zero, certain metals acquire infinite conductivity (zero resistance to the flow of charge). NASA Solar Panels

17. Electrical circuits have four basic parts: source, path, load, and switch Source: The power supply or battery Path: The wire Load: Lights, appliances, heaters Switch: Opens/closes the circuit

18. Simple Circuit Load Battery Path Switch

19. An electric bell is a simple circuit… When you flip the switch, the current flows through the wire to the electromagnet. From the electromagnet, it goes to the contact screw to the hammer.

20. Open Circuit Load Battery Path Path is disconnected.

21. Closed Circuit Load Battery Path Path is connected, switch is on.

22. Short Circuit Load Battery Path Path goes around the load.

23. Preventing Overloaded Circuits To prevent overloading in circuits, fuses are connected in series along the supply line. The entire line of current must pass through the fuse. The safety fuse is constructed with a wire ribbon that will heat up and melt at a certain current, this stops the flow when melted.

24. Fuses and Circuit Breakers  Fuses open the circuit and stop the flow of electricity.  Fuses cannot be reused once blown. o A circuit breaker uses bimetallic strips or magnets to open the switch. o Circuit breakers are used now because they can be reused and not thrown out.

25. Types of Circuits  Most circuits have more than one device that receives electrical energy. These devices are commonly connected in a circuit in one of two ways, series or parallel. series  When connected in series, they form a single pathway for electron flow between the terminals of the battery, generator, or wall socket. parallel  When they are connected in parallel, they form branches, each of which is a separate path for the flow of electrons.

26. Schematic Diagrams schematic diagrams Electric circuits are frequently described by simple diagrams called schematic diagrams. The positive terminal of the battery is represented with a long line and the negative terminal with a short line.

27. Drawing Circuits with Schematic Diagrams Series Circuit Parallel Circuit

28. Series Circuits o An electrical circuit in which devices are arranged so that charge flows through each in turn. o If one part of the circuit should stop the current, it will stop throughout the circuit. The more lights you have in a series circuit, the dimmer they are. A series circuit is like a single lane road with no alternate routes or paths.

29. Series Circuit Load Battery Path Loads are on same path.

30. Parallel Circuits o An electrical circuit in which devices are connected to the same two points of the circuit, so that any single device completes the circuit independently of the others. o If one part of the circuit should stop the current, the current will continue to the other parts of the circuit. All of the lights in a parallel circuit will have the same intensity. A parallel circuit is like a road with alternative routes. When one is blocked, you have other choices.

31. Parallel Circuit Load Battery Path Loads are on different paths.

32. Parallel Circuits and Overloading  Electricity is usually fed into a house by way of load wires called lines. These lines are very low in resistance and are connected to wall outlets in each room.  About 110 to 120 volts are impressed on these lines by generators at the power utility.  This voltage is applied to appliances and other devices that are connected in parallel by plugs to these lines.

33. Electric Current Electric Current:  The flow of electric charge Conduction Electrons:  Electrons that are free to move throughout the atomic network.  When electrons flow in a wire, the number entering one end is the same as the number leaving the other end.

34. What is Direct Current?  An electric current of constant direction. The flow of electrons goes only in one direction.  It is abbreviated DC.  A battery produces direct current What is Alternating Current?  Current that regularly reverses direction, flowing first in one direction and then in the opposite direction.  Power companies generate AC to make it easier to transmit electricity over long distances.

35. Voltage  When you rub a balloon on your hair it (the balloon) becomes negatively charged ~ several thousand volts! Ampere (Amp)  The SI unit for electric current (I)  a unit of electric current, or amount of electric charge per unit time, in coulombs per second.electric currentelectric chargecoulombs  The ampere is an SI base unit, and is named after André-Marie Ampère.SI base unit André-Marie Ampère  In practical household wiring terms, it is the measurement of the number of electrons passing through a given point in one second intervals

36. Voltage Sources

37. Sources of voltage  Dry cells, wet cells, and generators supply energy that allows charges to move. In dry and wet cells, energy released in a chemical reaction occurring inside the cell is converted to electric energy.  Generators, such as alternators in automobiles, convert mechanical energy into electric energy.

38. Electric Resistance  The amount of current that flows in a circuit depends on the voltage provided by the voltage source.  The current flow also depends on the resistance that the conductor offers to the flow of charge, which is called the electric resistance.  Thick wires have less resistance than thin wires.  Longer wires have more resistance than short wires.  Electric resistance also depends on the conductivity of the material and the temperature.

39. Ohm: Ohm’s Law: The relationship between voltage, current, and resistance.  This relationship states that you’ll get twice the current for twice the voltage. The greater the voltage, the greater the current. The greater the resistance, the less the current. Current Voltage Resistance

40. What is the current produced with a 9 volt battery through a resistance of 100 ohms? Solution: I=V/R I=(9 V)/(100 ohms) I=.09 Amps

41. What happens when there is less resistance to the current?  Low resistance permits a large current, which produces considerable heat.  If an appliance or circuit were to “overheat”, that means there isn’t enough resistance, and the electrons move too fast. It can catch on fire due to the intense heat.  Inside electronic devices such as radio and television receivers, the current is regulated by circuit elements called resistors.