Static Electricity

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

2. There are 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. Electric force  the force of attraction or repulsion between electrically charged objects

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

3. Where do charges come from? If electrons = protons neutral If electrons > protons  gaining electrons, negative charge Gains electron… negative ion =anion If electrons < protons  losing electrons, positive charge Loses electron… positive ion = cation

3. Where do charges come from? Electric field  effect an electric charge has on other charges

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

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

4. 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 Coulomb (C) SI Unit of electric charge 6.24 x 1018 electrons = 1 C Lightning = 10-20 C

5. 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.

6. 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 pushed away from the rod. - induced charges  top of the can: positive attraction + buttom of the can: negative & attraction > repulsion - metal can repulsion

6. Induction: The production of a charge in an uncharged body by bringing a charged object close to it Or… By contact or friction

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

Electricity Static

7. Static Discharge Human body can not feel less than 2,000 volts of static discharge Law of Conservation of Charge  total charge of a system is constant – charges can only be transferred

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

9. 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

10. 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 1.2x108 volts

Limit Exposure

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.

The End