Electricity

Electricity and Electrical Charges What is electricity? All the phenomena caused by positive and negative charges. Where do these charges come from?

Electrons: Nucleus: Located outside nucleus Contains protons (+1) & neutrons (no charge) Overall positive charge (+) Provides the biggest mass contribution (dense) Electrons: Located outside nucleus Easily moved, lost or gained Negative charge (-1)

Electrical Charges: - All matter has electrical charges There are two types of charges: Positive Negative + -

Only electrons can move from one object to another.  Negatively charged objects: contain more electrons(-) than protons(+). Positively charged objects: contain fewer electrons(-) than protons(+). Neutral objects: contain an equal #of protons(+) & electrons(-). Only electrons can move from one object to another. 

Ch 5. Electricity & Magnetism 5.1 Electrical Charge Write this in your notebook. Most objects are neutral because they have an equal # of protons (+) and electrons (-). Electrons can be transferred, this causes an object to become charged. Negative charge = object has more electrons than protons. Positive charge = object has more protons than electrons.

Law of Charges Attraction Repulsion There are 2 forces between charged objects: Attraction Repulsion Opposite charges “Opposites Attract” Same charges “Like repel” Law of Charges

- + Ex #1 A B A POSITIVE Opposites Attract! Sphere A is negatively charged. When placed beside sphere B, they attract. What is the charge on B? POSITIVE Opposites Attract! A B A - +

- + + + - + Ex #2 Attract A C A B B C Three charged spheres are suspended next to each other. If sphere A is negatively charged, what will happen when sphere A & C are suspended beside each other? Attract A C A B B C - + + + - +

+ + + - - + Ex #3 A B B C C D Repel Four charged spheres are suspended next to each other. What will happen if A & D were suspended next to each other? Repel A B B C C D + + + - - +

What would happen if “B” & “C” were brought together? You have three charged objects A, B & C in a lab. You record the following results: Ex #4 Test Observation Bring “A” near “B” They repel Bring “A” near “C” They attract + + + - + - What would happen if “B” & “C” were brought together? They would attract!!!

Charging Objects Most objects start out electrically neutral, but by CHARGING an object you create an imbalance in the number of electrons and protons; the object is then charged either positive or negative.

How do you charge an object? There are three ways to charge an object: 1. Charge by Friction 2. Charge by Conduction 3. Charge by Induction

Write this in your notebook. (5.1 continued) Write this in your notebook. One electron has a charge of 1.602 x 10-19 C. 1Coulomb (C) = the charge of 6.25 x 1018 electrons (-) or protons (+). Conductors permit the movement of electrons. (the charge spreads out quickly) Eg. Metals, graphite, electrolytic solutions Semiconductors slow the movement of electrons. Insulators stop the movement of electrons. Eg. Plastics, ceramics, wood, glass The triboelectric series (p146) is a list that ranks an object’s ability to take negative charges.

But which object gets the electron ??????? Charging by Friction When two neutral objects are rubbed against each other, one object may pull electrons away from the other creating one positive object and one negative object. But which object gets the electron ???????

Triboelectric Series: Please paste or copy the triboelectric series into your notes.

Triboelectric Series: Only negative charges move! Positive charges NEVER move!! Triboelectric Series: Triboelectric series is a list that ranks objects’ ability to take negative charges Rubber Ebonite Polyethylene Cotton Paper Silk Wool Glass Acetate Fur / hair Items at top take electrons (-) Add this to your notebook. Items at bottom lose electrons (-)

Items at top take negatives Ex #1 Your cat rubs against a rubber balloon. What will be the charge on the balloon? Your cat’s fur? Rubber balloon becomes negative Rubber Rubber Ebonite Polyethylene Cotton Silk Wool Glass Acetate Fur / Hair Cat’s fur becomes positive Fur / Hair Negatives

Polyethylene balloon becomes negative Items at top take negatives Ex #2 In a lab, you take a piece of neutral wool & neutral polyethylene & rub them together. What will be their charges? Polyethylene balloon becomes negative Rubber Ebonite Polyethylene Cotton Silk Wool Glass Acetate Fur / Hair Polyethylene Negatives Wool Wool becomes positive

In a lab, you rub a piece of cotton & ebonite together In a lab, you rub a piece of cotton & ebonite together. Then you rub a piece of silk & glass together. Ex #3 You then bring the charged piece of cotton & the charged piece of silk together. What will happen? Rubber Ebonite Polyethylene Cotton Silk Wool Glass Acetate Fur / Hair - Cotton is + Silk is - + - They would ATTRACT +

Ex #4 You rub your hair with a balloon. Explain using words & pictures, why your hair “sticks up”. 1st The hair & balloon are both neutral _ + _ _ + + 2nd The rubber balloon takes negative charges from the hair. So, the balloon becomes negatively charged & the hair becomes positively charged + _ + _ 3rd Since the hair is positive & like charges repel, the hair sticks up!!!

Write this in your notebook. 5.2 Static electricity. You can create a charge by causing electrons to be transferred from one item to another by: Friction. Items high on the triboelectric series pull electrons away from lower items. Conduction. Once in contact, a charged object can share its charge with another neutral object. Induction. Without contact! A charged object can cause the charges in a neutral object to shift to one side. See p147 Write this in your notebook.

Check for understanding Using pages 140 to 144 and your notes. Fill-in p75 & 76 of your workbook. If you don’t finish in class it is homework.

Charging by Conduction An object can be charged by touching it with another object that already has a charge. The resulting object will then have the same charge but weaker in strength than the original object.

Charging by induction objects do not touch (one is charged, one is neutral) Proximity of the charged object causes (induces) the charges in the neutral object to separate. See Fig. 5.17 in textbook.

Calculations: How do you measure “charge” Write this in your notebook. Calculations: How do you measure “charge” Ex. After charging a piece of fabric Kim determines that it has a charge of 9.1 C. How many electrons has it lost?        

Check for understanding finish for homework if necessary. An object has received 1.125 x 1019 electrons. What is its charge in Coulombs? How many electrons have been lost by an object whose charge is 4.1C? Does the object now have a positive or negative charge? A cotton sock and a wool sock have created a charge of 20.4C? Which sock receives the electrons and how many? A negatively charged object, having 31C of charge comes into contact with another neutral item. What is the resulting charge of each item? Positive or negative? Workbook p 77 (bottom only) p78 #1 & #2 only  Enjoy you weekend 

Check for understanding Using pages 145 to 149 and your notes. Fill-in p77 (bottom only) & p78 (#1 & #2 only) If you don’t finish in class it is homework.

Robert J. Van de Graaf 1929

These notes have covered: p140 to p148 in the text P75 to p78 in the workbook