Static Electricity What Is Static Electricity A stationary

Static Electricity

What Is Static Electricity? • A stationary electrical charge that is built up on the surface of a material

Where do charges come from? Matter is made up of atoms. + – neutron (neutral) + + – Proton (positive charge) + – atom – electron (negative charge) nucleus

Where do charges come from? If electrons = protons neutral If electrons > protons gaining electrons, negative charge If electrons < protons losing electrons, positive charge

Law of Electric Charges • The law of electric charges states that like charges repel, and opposite charges attract. • Protons are positively charged and electrons are negatively charged, so they are attracted to each other. • Without this attraction, electrons would not be held in atoms.

Electro-negativity +++++ +++ ++ + Relative electro-negativity ranking for some common materials from electron donating materials (+, glass) to -electron accepting --materials (-, teflon) ---- • • • Glass Human Hair Nylon Silk Fur Aluminum Paper Cotton Copper Rubber PVC Teflon

Electric Force The force between the charged objects is an electric force. The size of the electric force depends on 2 things: 1. 2. The amount of charge (the greater the charge, the greater the force) The distance between charges (the further the distance, the less the force)

Insulators and conductors Insulators: materials that do NOT allow electrons to flow through them easily. Insulators can be easily charged by friction as the extra electrons gained CANNOT easily escape.

Insulators and conductors • Conductors: materials that allow electrons to flow through them easily. Conductors CANNOT be easily charged by friction as the extra electrons gained can easily escape.

How Can You Charge Objects? There are 3 ways objects can be charged: 1. Friction 2. Induction 3. Conduction

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

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

Two kinds of charges • After being rubbed, a plastic ruler can attract paper scraps. Ruler carries electric charge. It exerts electric force on paper. This charging method is called charging by friction. The interaction between static electric charges is called electrostatics.

Induction: The production of a charge in an uncharged body by bringing a charged object close to it When negatively charged rod is put near a metal can. . . - - - induced charges attraction top of the can: positive buttom of the can: negative ++ + + metal can electrons of the can are pushed away from the rod. - - + - repulsion & attraction > repulsion

Attraction of uncharged objects Similarly, when charged rod is close to paper scrap. . . - - - - attraction between the attraction rod and + charge > repulsion between the rod and - charge. ––– – ++ + + paper molecules of paper align. repulsion

Conduction • Charging by conduction happens when electrons move from one object to another through direct contact (touching). Ex. Suppose you touch an uncharged piece of metal with a positively charged glass rod. Electrons from the metal will move to the glass rod. The metal loses electrons and becomes positively charged.

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?

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.

Grounding b How does grounding occur? + + + When we touch a metal ball of positive charge. . . – electrons flow from the earth to the metal ball to neutralize the metal ball. Metal ball becomes neutral.

Grounding How does grounding occur? – – – Similarly, if the metal ball is of negative charge. . . – extra electrons flow from the metal ball to the earth and the ball becomes neutral.

Lightning • kills more than 60 people and • injures more than 400 people a year in the US • one mile every five seconds • about 20, 000 C • Voltage of up to 1. 2 x 108 volts •

How Lightning Forms