1. Elementary Electrostatics
Rubbing a balloon on a wool jumper makes the balloon attract your hair
The balloon is said to be “charged” or to have an “electric charge”
Similarly glass rubbed with silk/fur will become “charged”
Charged glass will attract a charged balloon
Two charged balloons will repel each other

2. Types and Sources of Electric Charge
Two kinds of electric charge – positive
negative
protons
electrons
Quantum Mechanical Model
Bohr Model of Atom
Materials with equal numbers of neg. and pos. charge are
said to be electrically neutral.

3. Electric Charge
All ordinary matter contains both positive and negative charge.
You do not usually notice the charge because most matter contains the exact same number of positive and negative charges.
An object is electrically neutral when it has equal amounts of both types of charge.

4. Properties of Electric Charge
Charge is quantized.
Positive and Negative charges have same magnitude
e = p = 1.6 x C
SI unit of charge is the Coulomb
Charge is conserved.

5. Behaviour of Charges ‘Like’ charges repel
‘Unike’ or opposite charges attract
Q = + ne where n is a whole number

7. Seeing the effects of charge: the electroscope
the electroscope is a simple device for observing the presence of electric charge
it consists of a small piece of metal foil (gold if possible) suspended from a rod with a metal ball at its top
If a negatively charged rod is placed near the ball,
the electrons move away because of the repulsion.
The two sides of the metal foil then separate.

8. Different elements will have different
Atoms and Materials
Different elements will have different
types of bonds – different strengths.
Classification of Materials
– Conductors, Insulators, Semiconductors
Conductors
Electrons are free to move
about the material
Insulators
Electrons are bound to the atoms
- can’t move (conduct).

9. Different Methods of Charging
Friction e.g. rubbing a balloon with wool
Conduction e.g. touching an electroscope
Induction e.g. balloon sticking to a wall

10. How do we charge an object? Charging by rubbing
When two neutral objects are rubbed together, charge is transferred from one to the other and the objects become oppositely charged.
This is called charging by friction.
Objects charged by this method will attract each other.
A charged balloon will stick to a (neutral) wall or other insulating surface.
When a negatively charged balloon is near a wall, electrons inside atoms in the wall are repelled.
Since the wall is made of insulating material, the repelled electrons are not free to travel between atoms.
The electrons can move within each atom, so they spend more time on the side of the atom that is farthest from the balloon.

11. How do we charge an object?
Charging by rubbing
Conductors – charge will distribute around the surface to try
until equilibrium is achieved.
- charge only resides on surface, not inside.
On symmetric objects,
charge distributes uniformly
On non-symmetric objects,
charge collects at sharp points.
Insulators – charge cannot move,
so it remains localized
around the contact region.

13. Charge by Cnduction (contact)

14. Charge by Induction (no contact)

15. Charge is physically moved in/on the materials.
How do we charge an object?
B. Induction – Inducing a charge without touching.
Conductors
Charging by induction (two conductors)
Charging by induction (1 conductor and ground)
Charge is physically moved in/on the materials.

16. http://www. tutorvista

17. Atoms are randomly oriented
Induction (contd)
Insulators
Free Standing
Atoms are randomly oriented
Charge does not actually move
In/on the insulator – redistributes.
Polarizes the material.

18. Fields and forces
You can think of the field as the way forces are transmitted between objects.
Charge creates an electric field that creates forces on other charges.

22. Drawing the electric field

23. Lightning- outdoor spark
causes 80 million dollars in damage each year in the US
On average, kills 85 people a year in the US
over in a thousandth of a second
carries up to 200,000 A
causes the thunder!

24. development of a lightning bolt
charge
separation
stepped
leader
leader &
streamer
leader meets
streamer
lightning
bolt

25. applications of electrostatics
Xerox copiers use electrostatic attraction to put the ink droplets on the paper
electrostatic precipitators use the attraction of charged dust to remove dust particles from smoke.
can be used to hold balloons on your head

26. Removing soot particles
Positive
cylinder
Chimney
stack
Charging units
spray electrons
on the soot
particles
soot