Static Electricity

What Is Static

Electricity?• A stationary

electrical charge

that is built up on

the surface of a

material is called

static charge.

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.

• There are two types of charge:

– Positive (+) charge

– Negative (-) charge

• The SI unit of charge is the coulomb (C)

• Charges come from atoms.

• Atoms contain neutrons, protons and

electrons.

• Protons have a positive charge

• Electrons have a negative charge.

Where do charges come from?

Matter is made up of atoms.

++

+

–

––

+

–

Proton (positive charge)

neutron (neutral)

electron (negative charge)

atom nucleus

LAWS OF ELECTROSTATICS

• There are two (2) laws of electrostatics:

1. Like charges repel

2. Unlike charges attract

• Positive charges are attracted to negative

charges and negative charges attracted to

positive charges.

• Positive charges repel each other.

• Negative charges repel each other.

CONDUCTORS

• Materials that allow charges to pass through them are called conductors.

• There are good and poor conductors:– Good conductors conduct very well.

– Examples:• Metals especially silver, copper and aluminium

• Carbon

– Poor conductors do not conduct charge very well.

– Examples:• Water

• Human body

• Earth

Insulators

• Some materials do not allow charge to pass

through them. They are called insulators.

• Examples:

– Plastics

– Rubber

– Dry air

– Glass

Semiconductors

• Semiconductors are materials that are poor

conductors when cold and better conductors

when hot.

• Examples:

– Silicon

– Germanium

Electric field

• When a charge is brought near another

charge, it experiences a force (attraction or

repulsion)

• A region in which an electric charge

experiences a force is called an electric

field.

• In an electric field, lines move from the

positive to the negative charge. These lines

are called Electric field lines.

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

USES OF ELECTROSTATIC CHARGE

1. Electrostatic precipitators

2. Industrial inkjet printers

3. Photocopiers

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.

Grounding

++

++

+

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...

Grounding

–

–––

–

extra electrons flow from the metal ball to the earth and the ball becomes neutral.

The End