Unit II - Electricity

1. Unit II - Electricity

2. Introduction to Electricity Part I • Introduction to Electricity Part II

3. Introduction Activity • We will perform the following activities: • Observe the effect of rubbing a balloon against the wall. Explain • Observe the effect of rubbing a balloon against hair. Explain. • Observe the effect of bringing the balloon near a pop can. Explain.

4. Part 1. Electrostatics • Rubbing a balloon against your head does NOT create electric charges, the charges were already there! • all matter is made of atoms, and atoms are made of tiny particles which include electrons • When you rub a balloon against your head, electric charges are transferred from one object to the other

5. On many substances, the charge will remain after rubbing and not move or disappear • The word static means “unchanging”, so this type of electicity is called static electricity • The study of static electric charges is called electrostatics

6. A. The Electrical Nature of Matter • A plastic comb and a woolen sweater are both neutral (uncharged); this means they both have an equal number of positive and negative charges • When rubbed against each other, electrons are transferred from one to the other, creating • a positive charge on the wool sweater (lost electrons) • a negative charge on the comb (gained electrons) • Attraction & Repulsion

7. Law of Electric Charges • Like charges repel • (ex. + repels +) • Unlike charges attract • (ex. - attracts +) • Charged objects will attract neutral ones • (ex. + or – will attract neutral objects)

8. Mind-Bender • What is the charge of the following objects • Attracted to the comb, repelled by the wool sweater • Repelled by the comb, attracted to the sweater • Attracted to both the comb and the sweater

9. Model for the Electrical Nature of Matter • All matter is made of submicroscopic particles called atoms • At the center of each atom is a nucleus, with two kinds of particles, the positively charged protons and the uncharged neutrons; these particles do not move from the nucleus when an atom becomes charged • Ex. Bohr diagrams • A cloud of negatively charged particles called electrons surrounds the nucleus; an electron has an equal but opposite charge to a proton. When atoms become charged, the electrons can move from on atom to another

10. Like charges repel; unlike charges attract • In some elements (like copper), the electrons are not strongly attracted to the nucleus, and are more likely to move away; other elements (like Sulfur) have electrons tightly bound to the nucleus and are less likely to move. • In every atom, the number of protons are equal to the number of electrons; the net charge of the atom is zero • If an atom gains an electron it becomes negatively charged • If an atom loses an electron, it becomes positively charged

11. Question • Why does the attraction of two objects not prove that the objects are oppositely charged? Why is the “Repel” test more conclusive?

12. B. Charging by Friction • Charging by friction causes many of the effects produced by static electricity • Electrons are transferred by rubbing; but which way do the electrons go?

13. Electrostatic Series

14. Transfer by Contact • Transferring a charge by friction is difficult to avoid • natural tendency in nature towards balance and having a neutral charge • Electrons will actually jump before contact, like a miniature lightning bolt • The electrons will jump because they are trying to equalize the charge between the two substances

15. Question • How can you protect yourself from getting a shock? • Why would working in a grain elevator or flour mill be dangerous? • In what situations would charging by friction be dangerous? How would you protect yourself? • Would moving your hand very quickly to the doorknob prevent the shock? • How does a gasoline tank truck protect itself from static discharge?

16. Insulators and Conductors • Charges remain in the places where the friction occurred because these substances are electrical insulators • An insulator is a substance in which electrons cannot move freely from atom to atom • If electrons accumulate on an insulator, they will remain there until they are removed by some substance that exerts a greater force on the electrons • DYK? - When you rub glass or wood clean, you leave a static charge that attracts dust particles?

17. Because electrons cannot easily be transmitted though an insulator, they can protect us from an electric shock • The wires within an electrical cord are covered in a plastic/rubber coating (why?) • What other objects in your home use insulators to protect you from shocks?

18. A conductor is a substance in which electrons can freely move from one atom to another • If a conductor becomes charged, it will share and transmit the charge freely through the conductor • Metals are good conductors; no matter how much you polish a tap, it will never build up a static charge because the charge is immediately conducted away through the metal

19. Dry air is an insulator; water is a (poor) conductor • During the winter, the air is very dry; • During contact, moisture in the air will conduct the static charge away from the clothing • If there is no moisture, the static charge will be greater on the clothing

20. Discharging Electrical Objects • If a charged object has its excess of electrons removed, it has been dischargedor neutralized • When a charged object is connected to the Earth, it shares its charge with the whole earth; this is called grounding • Moisture in the earth is a good conductor, and whatever electric charge exists is distributed throughout the earth, making it harmless. • The third post in an electrical plug is the ground • Electric FencePeeing on an Electric Fence

21. Assignment/Quiz #2 • What is the difference between a conductor and an insulator? (2 marks) • Why does a spark occur when a person who is charged touches an uncharged object? (2 marks) • What is a ground? Explain. (2 marks) • Why are static electricity problems more common in the winter? (2 marks) • Why does lightning discharge from the clouds to the earth? (2 marks)

22. DYK  The friction from rubbing your feet on carpet produces a charge that can be in excess of 15,000V; the shock is small because there isn’t a significant amount of charge to be dangerous (amperage)

23. Induction • Induction is the transfer of electrons without direct contact • This differs from charge by friction or contact where objects touch one another • As a piece of dust approaches a TV screen, the electrons on the dust particles are forced to change position (repelled by the electrons on the surface of the TV) • This induced charge on the dust particle (recall: the electrons pushed to the other side of the dust particle), the positive charges that remain are strongly attracted to the TV • Draw a diagram

24. This induction is why neutrally charged object are always attracted to charged objects • Next time you’re at home, hold a magnet up to the TV screen, observe. How do the electrons on the TV screen react to the magnet?

25. Uses for Static Electricity • Since dust is attracted to static electricity, dust filters have been invented that rely on this principle, cleaning the air • By using charged paint on an oppositely charged surface, it is possible to reduce waste and increase efficiency when painting products like automobiles or trains • A photocopier uses this principle to attach dry ink to paper

26. Lightning • Observe Lightning Video Montage

27. Electricity and Electric Circuits • The movement, or flow, of an electric charge from one place to another is called an electric current • There is a key difference between the electricity flowing through a circuit and the electricity flowing through lightning; the current flowing through a circuit is in a controlled path called an electric circuit • Electric circuits are used to convert electricity into other forms of energy we need in our daily lives

28. Parts of an Electric Circuit • Source of electrical energy • Many advancements in technology revolve around creating new way of producing electric energy • They range from small amounts needed to run a small device like a wristwatch to large amounts generated at nuclear power stations • In between these are such sources as photoelectric cells used in calculators, cells and batteries, portable generators and wall outlets • Question: Where does our power come from in Saskatchewan?

29. Electrical Load • An electrical load is simply the given name to anything that converts electric energy into whatever form of energy we need (heat, motion, etc.) • A light bulb and a toaster are examples of electrical loads

30. Electric Circuit Control Device • Switches are the simplest form of control for electric circuits; however, there are many that we don’t see inside of appliances in our home • The clock timer in your microwave or the thermostat that controls the temperature of your home are examples of this

31. Connectors • Connectors provide a controlled path for the electric current to flow to each part of the circuit • Connectors are made of very conductive metals like aluminum, copper, gold and platinum; they can be as wide as transmission lines or 10,000 times thinner than a human hair • The microchip has connecting wires so small they are often only a few atoms wide

32. Connecting wires are usually drawn as straight lines with right-angled corners • A cell consists of a long line followed by a short bold line; the long line is the cathode (positive) and the short end is the anode (negative) • 2 cells or more in a row are called a battery

33. Assignment • Draw a 2 cell circuit with a closed switch and a motor • Draw a 4 cell circuit with an open switch and a light bulb • Draw a 3 cell circuit with two switches, each followed by a light bulb • Which bulbs are lit up? Indicate with lines of light emanating from the bulb

34. Assignment • Complete the following handout

35. Electricity Project • Electricity is a dynamic form of energy, capable of making our lives easier, more comfortable and safer. • Some sample questions that will be addressed: • Where does this energy come from? • How is it made? • Who uses which technology in Canada? • Which technologies use renewable resources? • What is ‘green’ energy? • The following project will address these questions and more; as the future of Canada it is important for you to be educated about where energy comes from, as you will play a role in deciding the future course of Canada’s energy policies (Yikes! Better make an intelligent decision!)