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

CORE CONCEPTS Static electricity (AKA Static Charge) refers to the build-up of an electric charge on the surface of objects that is waiting to be released. It does this by the gain/loss of electrons. Discharge occurs once you bring a charged object near another non charged object, the amount of electricity is released. The Laws of Static Charge explain how objects will move in relation to each other based on their electric charges. Coulomb’s Law is a set of relationships that describe how electric force depends on the types, distance and strength of charges.

STATIC ELECTRICITY Static electricity is the build up of an electric charge on the surface of objects. It is caused by an imbalance of positive and negative charges, caused by friction, when electrons move within or are transferred between different materials. An electric charge results from an increase or decrease in the number of electrons.

The Atom Nucleus: Contains protons (+) & neutrons (no charge) Overall positive charge (+) Contains nearly all mass (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

Electrical Charges 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.

Electrical Charges 6 protons, 6 electrons = neutral charge 6 protons, 5 electrons = positive charge 6 protons, 7 electrons = negative charge

LAWS OF STATIC CHARGE Objects with opposite charges attract each other. Objects with the same charge repel each other. Neutral objects are not attracted to charged objects.

- + Example #1 A A B B 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 A B B - +

- + + + - + Example #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 - + + + - +

+ + + - - + Example #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? Example #4 You have three charged objects – A, B & C in a lab. You record the following results: 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!!!

THE TRIBOELECTRIC SERIES CHART The Triboelectric Series chart shows how materials are ranked by their tendency to gain or lose electrons when rubbed with other materials. (page 276 textbook) If two materials are rubbed together, the one higher on the list gives up electrons and become positively charged. The material lower on the list will gain those electrons and become negatively charged. Factors that can affect the ability of materials to hold charges: humidity, surface roughness and rubbing force.

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