1. By Mr. Chaiporn Pattanajak
Banphue pittayasan School
Facebook.com/chaiporn.pattanajak
084-9250671 , 082-7364148

2. I. Electric Charge, Forces, and Fields
II. Electric Potential
III. Capacitance
This lesson we learn about

3. Around the outside of an
atom are electrons, which
have a negative charge.
An atom has equal amounts of negative and positive
charges, which balance each other, so the atom has
no overall charge.
Where does static charge come from?
The nucleus at the centre of
an atom contains protons,
which have a positive
charge.
Electrons do not always stay attached to atoms
and can sometimes be removed by rubbing.

4. Charging by Friction
• A Styrofoam
plate when
rubbed with
wool gets
charged by
friction.

5. Ways to Charge an Object
• Friction:
–When two objects come
in contact, one object
may lose electrons
–The other object will
gain them!
–How easily an object
gains or loses electrons
depends on what it is
made of!

6. Electric Charge
Like charges repel; unlike charges attract.
As with Mass/Energy: Charge is conserved
The net charge of an isolated system remains constant.
This is another fundamental law in physics

7. Properties of Charges

8. Properties of Charges
Like charges repel,
Unlike charges attract.
+ +
+ -

9. Electric Charge
SI unit of charge: the coulomb, C. All charges
in nature are integer multiples of the charge on
the electron:

10. Conductors
Most atoms hold on to their electrons tightly and are
insulators. In aluminum, the valence electrons are
essentially free and strongly repel each other. Any external
influence which moves one of them will cause a repulsion of
other electrons which propagates, "domino fashion" through
the conductor.
In a conducting material,
the outer electrons of the
atoms are loosely bound
and free to move through
the material.

11. Conductors
Property of material: conductivity
1.Conductors transmit charges
readily.
2.Semiconductors are
intermediate; their conductivity
can depend on impurities and can
be manipulated by external
voltages.
3.Insulators do not transmit
charge at all.

12. Electric charge is conserved
– the arithmetic sum of the
total charge cannot change in
any interaction.
Static Electricity; Electric
Charge and its Conservation

13. METHODS OF CHARGING
1. Charging by Friction
•Transfer of electrons between the two objects that are rubbed
together.
•Material losing electron is positively charged and material gaining
electron is negatively charged.
•Amount of gained and lost electron is equal to each other.
.
METHODS OF CHARGING
1. Charging by Friction
•Transfer of electrons between the two objects that are rubbed
together.
•Material losing electron is positively charged and material gaining
electron is negatively charged.
•Amount of gained and lost electron is equal to each other.
.

14. Conductor:
Charge flows freely
Metals
Insulator:
Almost no charge flows
Most other materials
Some materials are semiconductors.
Insulators and Conductors

15. Metal objects can be charged by conduction:
2. Charging by Conduction

16. They can also be charged by induction, either
while connected to ground or not:

17. Nonconductors won’t become charged by
conduction or induction, but will experience
charge separation:

18. The electroscope
can be used for
detecting charge:
The Electroscope

19. Electrostatic Charging
Objects can have excess charge of one polarity or another.
An electroscope may be used to determine if an object is
electrically charged.

20. Charging by conduction
An electroscope can
be given a net
charge by conduction
– when it is touched
with a charged
object, the excess
charges flow freely
onto the
electroscope.

21. The charged electroscope can then be
used to determine the sign of an unknown
charge.

22. Charging of
two bodies by
induction when
they are in
contact with
each other.
3. Charging by Induction
•Method used to charge an object without actually
touching the object to any other charged object.
3. Charging by Induction
•Method used to charge an object without actually
touching the object to any other charged object.

23. Charging by Induction
• There is no contact with the charging body.

24. Charging by Induction

25. Charging by Induction

26. Charging by induction
• In charging by
induction, a charged
body A imparts some
charge to another body
B without any actual
contact between the
two.

27. To charge a single metal conductor
by induction

28. To charge a single metal conductor
by induction

29. To charge a single metal
conductor by induction

30. To charge a single metal
conductor by induction

31. Polarization of a Cloud
Detailed Lightning
One mechanism incorporates friction: when moist, warm air rises, it
cools and water droplets form. These droplets collide with ice crystals
and water droplets in a cloud. Electrons are torn off the rising water
droplets by the ice crystals. The positive droplets rise to the top of the
cloud, while the negative ice crystals remain at the bottom.
A second mechanism involves the freezing process: experiments have
shown that when water vapor freezes the central ice crystal becomes
negatively charged, while the water surrounding it becomes positive. If
rising air tears the surrounding water from the ice, the cloud becomes
polarized.
There are other theories as well.
Lightning is the discharge of static
electricity on a
massive scale. Before a strike the bottom
part of a
cloud becomes negatively charged and the
top part
positively charged. The exact mechanism
by which this polarization (charge
separation) takes place is uncertain, but
this is the precursor to a lightning strike
from cloud to cloud or cloud to ground.

32. Lightning Strikes
The negative bottom part of the cloud induces
a charge separation in the ground below. Air
is normally a very good insulator, but if the
charge separation is big enough, the air
between the cloud and ground can become
ionized (a plasma). This allows some of the
electrons in the cloud to begin to migrate into
the ionized air below. This is called a “leader.”
Positive ions from the ground migrate up to
meet the leader. This is called a “streamer.”
As soon as the leader and streamer meet, a
fully conductive path exists between the cloud
and ground and a lightning strike occurs.
Billions of trillions of electrons flow into the
ground in less than a millisecond. The strike
can be hotter than the surface of the sun. The
heat expands the surrounding air; which then
claps as thunder.
+ + + + + + + + +
- - - - - - - - -
+
+
+ + +
++ + +

33. A Van de Graaff generator consists of a large metal dome attached to a tube,
within which a long rubber belt is turning on rollers. As the belt turns friction
between it and the bottom roller cause the e-
’s to move from the belt to the roller.
A metal brush then drains these e-
’s away and grounds them. So, as the belt
passes the bottom roller it acquires a positive charge, which is transported to the
top of the device (inside the dome). Here another metal brush facilitates the
transfer of electrons from the dome to the belt, leaving the dome positively
charged.
In short, the belt transports electrons from a metal dome to the ground, producing
a very positively charged dome. No outside source of charge is required, and the
generator could even be powered by a hand crank. A person touching the dome
will have some of her e-
’s drained out. So, her lightweight, positive hair will repel
itself. Coming close to the charge dome will produce sparks when electrons jump
from a person to the dome.
Van de Graaff
Generator
Internal workings Detailed explanation