1. Static electricity

2. An object can store electric charges that cannot flow
An object can store electric charges that cannot flow. These charges are called STATIC CHARGES.

3. Where do these charges come from?
All the materials made up of tiny particles called ATOM.
An atom contains electrons, protons and neutrons
Electrons orbit the nucleus
Protons and neutrons are collectively known as nucleons
Neutrons have no charge, electrons are negatively charged and protons are positively charged.
Since an atom is neutral the number of protons is equal to the number of electrons.

4. So there are two types of charges
That are positive (+)(proton) and negative (−)(electron) charges.
Charges are measured in units called COULOMBS (C).
CHARGING BY FRICITON
Rub a plastic ruler with a piece of cloth and then hold it near some tiny pieces of paper. The rubbed plastic ruler attracts the piece of paper.

5. Rub a balloon with a piece of cloth and then hold it near (but not touching) a thin stream of water from tap. The rubbed balloon attracts the stream of running water.
Because of friction with piece of cloth,
The plastic objects have been CHARGED
with STATIC ELECTRICITY.

6. When a cloth rubbed with a Perspex rod it becomes positively charged as shown below. Before rubbing

7. After rubbing
The perspex rod becomes positively charged and the cloth becomes negatively charged, that is because from the rod electrons transferred into cloth. So there are net positive charge in rod and net negative charge in cloth.

8. When a cloth rubbed with polythene rod it becomes negatively charged as shown below.
Before rubbing

9. After rubbing
The polythene rod becomes negatively charged and the cloth becomes positively charged, that is because from the cloth electrons transferred into rod. So net negative charge in rod and net positive charge in cloth.
So the charging of solid object involved transfer of electrons from object to another.

10. Charging by induction
When positively charged rod is brought near to an uncharged conducting sphere. The electrons in the sphere pulls towards the rod, which leaves the other side of the sphere with net negative charge. This is called charging by induction.
Reverse happens when negatively charged rod is brought near to an uncharged conducting sphere. The electrons in the sphere repels on the other side of the sphere, so the net positive charge left near to the rod.

11. A negatively charged polythene rod is suspended by using thread
A negatively charged polythene rod is suspended by using thread. When positively charged perspex rod is brought suspended polythene rod. Polythene rod moves towards perspex rod.
This means unlike charges attract.

12. A negatively charged polythene rod is suspended by using thread
A negatively charged polythene rod is suspended by using thread. When another negatively charged polythene rod is brought suspended polythene rod. Both polythene rod moves away from each other.
This means like charges repel.

13. Electric field
Electric field is a region in which an electric charge experiences a force.
We can show electric fields by lines with arrows (called ELECTRIC FIELD LINES).
Electric field lines due to single charge

14. Electric field lines between like charges
Electric field lines between unlike charges

15. Conductors Insulators
Conductors are materials that allow electric charges to flow through them easily. They have large number of free electrons that can move easily from atom to atom e.g. metals ( e.g. copper, aluminium, steel, iron) etc..
Insulators
Insulators are materials that do not allow electric charges to flow through them easily.
The electrons are tightly bound to the atoms and they are not free to move.
e.g. plastic, rubber, wood, glass etc..

16. Dangers of static electricity
Lightning
In a thunderstorm, the clouds are charged by friction with air current. When charged cloud comes above the buildings, trees and ground, the buildings trees and ground induces opposite charge as in cloud. So the large potential difference between cloud and Earth is produced, as a result electrons moves through the air and collide with air molecules in the air and cause them to give out lightning flash. It can burn forests, damage houses and kill peoples.

18. Refueling
When the oil tanks are refueling, the oil and refueling pipe may charge up because of the friction. So the charges build up may collide with each other and spark produce, which leads to catch the fire in the oil tank. So to stop building up the charge, the oil tank must be earthed.

19. Lightning conductor
Tall buildings usually have a strip of copper called a lightning conductor attached at the top of the building and connected to the Earth. This lightning conductor catches the unwanted electrons flow through the air due to charged cloud and provides route for electrons to pass into the ground without damaging the building.

20. Earthing
Connecting a conductor to the charged object to remove unwanted charges.

21. uses of static electricity
Electrostatic precipitator
When dust and ash particles move upward, the dust and ash becomes negatively charged by coming into contact with wires. Since unlike charges attract, the dust and ash move and stick to the positively charged plate. The dust and ash is now remove from the hot gases and hot gases released into air.

22. Photocopy machine

23. Electrostatic spraying
Bicycles and cars always painted by using electrostatic spraying. The paint is given a charge and this makes better spray. The droplets all have the same charge and repel each other so that the paint spreads out to form a large even cloud.
The charged droplets are all attracted to the object and stick strongly to the surface because it has an opposite charge. Hence less paint is needed and less paint is wasted.