Static Electricity

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.

The interaction between static electric charges is called electrostatics.

This charging method is called charging by friction.

Where do charges come from?

Matter is made up of atoms.

+++

–

––

+

–

Proton (positive charge)

neutron (neutral)

electron (negative charge)

atom nucleus

If electrons = protons neutral

Where do charges come from?

If electrons > protons gaining electrons, negative chargeIf electrons < protons losing electrons, positive charge

Electro-negativity

Relativeelectro-negativityranking for somecommon materialsfrom electron donatingmaterials (+, glass) toelectron acceptingmaterials (-, teflon)

• Glass• Human Hair• Nylon• Silk• Fur• Aluminum• Paper• Cotton• Copper• Rubber• PVC• Teflon

+ + + + ++ + + ++ + ++ ++

-- -- - -- - - -- - - - -

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...

Where do charges come from?

– electrons are pulled from the wool to the balloon.

The balloon has more electrons than usual.

+++++

–––––The balloon: – charged, The wool: +charged

wool

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 pushed away from the rod.

top of the can: positive

& attraction > repulsion+++ ++

metal can - -

---

----- --

buttom of the can: negative

induced charges

attraction

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.paper +–+–+–+–

+–+–+–+–

attraction

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.

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 a woollen cloth.

2 During rubbing, what have been transferred between the woollen cloth and the balloon?

A Electrons B Protons

C Neutrons

A balloon has a negative charge when rubbed by woollen cloth.

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.

How does a positively charged rod attract a neutral object?

negative chargepositive charge

attractionrepulsion

Grounding

An object is grounded when it is connected to the earth through a connecting wire.

What is grounding?

If a charged conductor is grounded, it will become neutral.

Groundingb 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.

Similarly, if the metal ball is of negative charge...

GroundingHow does grounding occur?

–––––

–

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.

frictionsparks

explosion

ground

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 NowWrite 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