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

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

Negatively charged objects: contain more electrons (-) than protons (+). Positively charged objects: contain fewer electrons (-) than protons (+). Only negatively charged electrons can move from one object to another and if you have an equal number of protons and electrons, the object is neutral.

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

Write this in your notebook. Law of Charges Write this in your notebook. Opposite charges attract Like charges repel

Activity Stations At each station please paste the question into your notebook (leaving room so the questions can be ordered numerically 1-5). Then answer the question in your notebook and explain your answer (DO THIS IN PENCIL!) Wait at that station until instructed to move. We will review the answers together.

- + 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!!!

Ex #5 An atom becomes negative when: What particles in an atom have an electric charge? Neutrons and protons Protons and electrons Electrons and neutrons None of the above An atom becomes negative when: A proton leaves the atom An electron joins the atom An electron leaves the atom A proton joins the atom A proton and an electron leave the atom An object becomes electrically charged when: Electrons are created in it Protons are created in it Electrons from it are destroyed Electrons leave or join it Protons from it are destroyed

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

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.

Triboelectric Series: All objects begin neutral & can become positively or negatively charged A positively charged object has more positives than negatives A negatively charged object has more negatives than positives How does an object become charged?

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 (-) Write this in 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!!!

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.

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.

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” The unit of measure for electrical charge is the Coulomb (C). In equations it is symbolized by a “q” Eg: q = 900C Ex. After charging a piece of fabric Kim determines that it has a charge of 9.1 C. How many electrons has it lost?        

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 their movement. Insulators stop their movement electrons. Eg. Plastics, ceramics, wood, glass The triboelectric series (p146) is a list that ranks an object’s ability to take negative charges.

Robert J. Van de Graaf 1929

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.

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