What Is Static Electricity? • A stationary electrical charge that is built up on the surface of a material
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.
+ + – – – – + + Where do charges come from? Matter is made up of atoms. Proton (positive charge) neutron (neutral) electron (negative charge) nucleus atom
Where do charges come from? If electrons = protonsneutral If electrons > protons gaining electrons,negativecharge If electrons < protons losing electrons,positive charge
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 Electro-negativity + + + + + + + + + + + + + + + - - - - - - - - - - - - - - -
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... electrons are pulled from the wool to the balloon. The balloon has more electrons than usual. wool The balloon: – charged, The wool: +charged
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.
4 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.
- - - - - - - + + + + + - - - - - 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... electrons of the can are pushedaway from the rod. induced charges top of the can: positive attraction buttom of the can: negative & attraction > repulsion metal can repulsion
- - - - - - - – – – – – – – – + + + + + + + + Attraction of uncharged objects Similarly, when charged rod is close to paper scrap... molecules of paper align. attraction between the rod and + charge > repulsion between the rod and - charge. attraction paper repulsion
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?
Gas Station Fires • Carol said a static gas pump fire is blamed for burning her daughter so badly she needed skin grafts on her legs. • Carol had put the gas pump nozzle on automatic and re-entered her car to write a check. When her then-12-year-old daughter, wearing a sweater and jacket that may have created static electricity, reached for the nozzle, flames suddenly ignited her clothing.
A balloon has a negative charge when rubbed by a woollen cloth. 1 If the balloon can attract some paper scraps, which of the following cannot be the charge of paper scraps? A Neutral B Positive C Negative
A balloon has a negative charge when rubbed by woollen cloth. 2 During rubbing, what have been transferred between the woollen cloth and the balloon? A Electrons B Protons C Neutrons
How does a positively charged rod attract a neutral object? When a + charged rod is put near neutral object, ______________ is induced on the side of the object near the rod and _____________ is induced on the side away from the rod. The rod can attract the netural object because _________ between rod and – induced charge > the ________ between rod and + induced charge. negative charge positive charge attraction repulsion
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. – – –
Why do gasoline tankers usually have metal chains at the back? When cars run, their tires and bodies are usually charged by _______. For gasoline tankers, if the accumulated charge is large enough, _______can be produced and _________ will occur if gasoline vapor is ignited. Those metal chains conduct the charge on the bodies of tankers to the _______ and avoid the danger. friction sparks explosion ground
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 1.2x108 volts Lightning
Do Now Write a paragraph about the cartoon. Tell what he is trying to do. Will it work and why? What do you think will happen? Use the following words, static electricity, lightning, electrons, positive and negative charges.