Static electricity is a stationary electric charge built up on the surface of materials. It is caused by electrons being transferred between two objects during friction. There are two types of charges - positive and negative. Atoms contain protons which have a positive charge and electrons which have a negative charge. The laws of electrostatics state that like charges repel and unlike charges attract. Materials that allow charge to pass through are conductors, while insulators do not. When a charged object is brought near an uncharged object, the electric field can induce charges in the uncharged object. Some applications of static electricity include electrostatic precipitators, printers, and photocopiers. Grounding neutralizes charged objects by connecting them to the earth.

1. Static Electricity

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

3. 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.

4. • 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.

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

6. 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.

8. 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

9. Insulators
• Some materials do not allow charge to pass
through them. They are called insulators.
• Examples:
– Plastics
– Rubber
– Dry air
– Glass

10. Semiconductors
• Semiconductors are materials that are poor
conductors when cold and better conductors
when hot.
• Examples:
– Silicon
– Germanium

11. 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.

13. • In an electric field, lines move from the
positive to the negative charge. These lines
are called Electric field lines.

14. 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

15. 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

16. USES OF ELECTROSTATIC CHARGE
1. Electrostatic precipitators
2. Industrial inkjet printers
3. Photocopiers

17. 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.

18. 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.

19. 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.

22. The End