Electricity

1. Electricity Static, Currents, Circuits

2. Electricity? • Electricity is all about electrons, which are the fundamental cause of electricity • Static Electricity - involves electrons that are moved from one place to another, usually by rubbing or brushing • Current Electricity - involves the flow of electrons in a conductor

3. Electricity Everything in the world is made up of atoms. Each atom has smaller parts in it. One of those parts is called electrons. Electrons can move from atom to atom. When an electron moves to a different atom, it causes another electron to have to move. When electrons move quickly from one atom to another is it called Electricity!

4. Let Us Review • ATOMS………………………………….

5. Atoms… • Have neutrons, protons, and electrons. • Protons are positively charged • Electrons are negatively charged

6. Electrons… • Are located on the outer edges of atoms…they can be moved. • A concentration of electrons in an atom creates a net negative charge. • If electrons are stripped away, the atom becomes positively charged.

7. The world is filled with electrical charges: + - + + + - + - - + + + - - - + + - - -

8. What is this electrical potential called? • Static Electricity - - - - - + + + - - + +

9. Static Electricity • The build up of an electric charge on the surface of an object. • The charge builds up but does not flow. • Static electricity is potential energy. It does not move. It is stored. • When static electricity is discharged a “spark” or “shock” occurs.

10. Static electricity • Static electricity is caused when certain materials are rubbed against each other. • Electrons can be rubbed off one material and on to another. • The material that has got extra electrons is now negatively charged • The material which has lost electrons is positively charged.

11. Where do charges come from? Rubbing materials does NOT create electric charges. It just transfers electrons from one material to the other.

12. + + – – – + – – + – + Where do charges come from? When a balloon rubs a piece of wool... electrons are pulled from the wool to the balloon. The balloon has more electrons than usual. wool The balloon: – charged, The wool: +charged

13. Static Discharge… • Occurs when there is a loss of static electricity due to three possible things: • Friction - rubbing • Conduction – direct contact • Induction – through an electrical field (not direct contact)

14. Static Discharge Human body can not feel less than 2,000 volts of static discharge Static charge built up by scuffing shoes on a carpet can exceed 20,000 volts?

15. The Electrostatic Force • The electrostatic force is simply the field force that exerted by electrical charges • Because of the intensity of the attraction between charged atoms, it is stronger than the force of gravity

16. Static Electricity Static electricity is the charge that stays on an object. Law of Charges Unlike charges attract each other, and like charges repel each other.

17. Electrical Charge • Some materials have a weak affinity (attraction) for electrons so they easily loose their electrons due to friction. When you walk across the floor you pick up these electrons and become “charged”. When you touch someone you release that charge (discharge) and shock them.

18. Electrical Charge • Most objects are neutral because their charges are balanced, but when conditions change so do the electrical charges • Have you noticed how on drier days you seem to pick up charges more easily and can “shock” your friends easily?

19. Electrical Charge • The reason some materials seem to have more ability to cause “shock” is because some materials have a weaker affinity for electrons • They give up their electrons more easily • When you walk across carpet your shoes/socks are able to pick up the electrons because the carpet easily gives them up • The you can SHOCK your friends

20. Electrical Charge • When an object loses electrons it becomes positive • A gain of electrons results in a negative charge • Whether a charge is negative or positive, the net charge is measured in Coulombs (C) • One Coulomb is the charge carried by 6.24 x 1018 protons or electrons

21. Electrical Charge • Remember insulators? • The reason they insulate so well is because they hold so tightly to their electrons (not allowing them to flow) • Conductors? • Conductors conduct so well because they hold loosely to their electrons allowing electrons to flow

22. Electric Fields • Electrostatic force is a field force- • Meaning that it is exerted over an area • Charged objects can exert a force on distant charges which they are not in direct contact • Physicists have noticed that electrical charges flow in a particular pattern • Lines of force radiate outward from a charged object through a path of least resistance

23. Electric Fields • The area around electric charges that has the force of the charge exerted on it. • When a charge is placed in an electric field, it is pulled or pushed. • The field is the strongest near the charged particle.

24. Electrical Induction • Is the creation of charge region when a neutral object when exposed to a nearby electrical charge • They do NOT touch • The charge is temporary • It is a field force

25. Electrical Induction • Dipole- contains a positive and a negative pole (end) • it is a neutral molecule whose electrons have shifted from positive to negative

26. Detecting Charges • Electroscope- an instrument used to detect the presence of a charge • They do NOT detect type of charge nor amount • It cannot quantify

28. Conductors vs. Insulators • Conductors – material through which electric current flows easily. • Insulators – materials through which electric current cannot move.

29. Transferring Charges • Electrical conductors- allow electricity to flow through, because they hold their electronsloosely • Most often these are metals • Remember that sea of electrons • Electrical insulators- do not allow electricity to flow, because they hold onto their electrons very tightly • Glass, wood, and rubber

30. Transferring Charges • Remember when you get rid of your stored electrons you are discharging the surface • Electrical discharge causes the shock you experience after a build up of static electricity

31. Transferring Charges • Semiconductors- allows limited electron flow or conduct under certain conditions • This is because some materials can change their electron affinity in response to environmental conditions

32. Conductors: Metal Water (only because of the minerals and metals in the water) Insulators: Styrofoam Rubber Plastic Paper Wood Examples

36. Grounding What is grounding? An object is grounded when it is connected to the earth through a connecting wire. If a charged conductor is grounded, it will become neutral.

37. Grounding • Additional wire in circuit to protect a person from shock. • Plugs have a 3rdprong. This connects the metal shell of the appliance to the groundwire of the building.

38. Lighting Rods • Lightning rods were used to protect buildings from lightning strikes • Lightning rod- metalrod mounted to the roof of a building. If lightning strikes the rod the energy flows down the rod to a ground wireand then into the Earth.

39. Storing Charges • How can we make an object keep its charge? • Remember insulators keep their electrons while conductors allow their electrons to flow freely……

40. Storing Charges • So… • To store a charge we must use both conductors and insulators…….

41. Storing Charges • Leyden jar- one of the first devices used to store charges • It is made of a jar (glass or plastic) lined and coated with lead and that used electrical induction and grounding to greatly increase storage capacity • Other metals will work, with less power

42. Storing Charges • Capacitors are devices used to store electrical energy today. • They are constructed very similarly to a Leyden Jar

43. How do we apply our knowledge of static electricity? • Pollution is a huge problem today, especially in big cities and in homes • Just like every other material even dust and other pollutants have atoms; and thus protons and electrons • Ionic purifiers clean the air by using electricity to attract and trap dust by generating negative ions. The negative ions are created by running high voltage electricity through thin metal plates that create a negative charge on surrounding gas molecules and adhere to the particulates in the air. Now that the particulates are linked with a negative charge, they are attracted to their opposite polarity, a positively charged metal plate that captures the impurities from the passing air flow.

44. Electrical Current and Ohm’s Law

45. Electricity that moves… • Current (electricity): The flow of electrons from one place to another. • Measured in amperes (amps) • Kinetic energy

46. Electrical Current • Electrical potential energy is the ability to allow electricity to flow • Conventional current flow- the flow of positive charges through a conductor, this is opposite the flow of electrons

47. Electrical Current • Conventional flow- flow of positive charges through a conductor • Let us look at this more.. • Now we know that protons do not move. This idea does not change that rule • What occurs when an electron leaves an atom, it leaves a positive hole. This causes an electron to move into it and another electron moves out in a different direction • So we can say that conventional current is movement of positive “holes” through a conductor

48. Current • The directed movement of electrons or the flow. (pushed by voltage) • Unit of measure is the amp or ampere • Measured with an ammeter or amp meter

49. Conventional theory Says that current flows from + to - Scientists first guessed that it was the proton that was in motion in the atom

50. Electron theory Says that current flows from – to + When scientists discovered that it was the electron that was in motion, electron theory was born