1. Daily phenomena Basic Definitions 1 Electrostatics
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Daily phenomena
“Charge” plastic materials by friction
Experience of electric force and electric charge
Repulsive and attractive electric force
Different kinds of charge : positive (+) and negative (-)
General Rule : like charges repel; unlike charges attract

2. Nature of charges Basic Definitions 2 Electrostatics
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Nature of charges
Structure of atoms and matter
Diagram
Balance of charge : no. of electrons = no. of protons
Neutral : no. of electrons = no. of protons
Diagram
Positively charged : no. of electrons < no. of protons
Negatively charged : no. of electrons > no. of protons
Charging by changing the no. of electrons only

3. Nature of charges Basic Definitions 3 Electrostatics
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Nature of charges
Unit : Coulomb (C)
Insulators (like plastics) : do not allow electrons to flow through them or escape easily
Conductors (like metals) : allow electrons to flow through them or escape easily
Charging by friction
Diagram
Induced charge
Diagram

4. Different ways of charging
Electrostatics
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Different ways of charging
Charging by extra high tension power (EHT) supply
Photo
Charging by Van de Graaff generator
Photo
Charging by sharing
Diagram
Charging by induction and separation
Diagram
Charging by induction and earthing process
Diagram

5. Nature of electric field
Electrostatics
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Nature of electric field
Presence of electric field : experience of electric force by a small charge around a charged object
Representation of electric field : field lines
Electric field pattern around a positive charge
Diagram
Electric field pattern around a negative charge
Diagram
Various electric field patterns
Diagram
Experimental setup to demonstrate electric fields
Photo

6. Application of charges
Applications 1
Electrostatics
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Application of charges
Action of a point
Diagram
Lightning conductor and action of a point
Diagram
Electrostatic precipitation
Photocopying

7. Electrostatic hazards
Applications 2
Electrostatics
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Electrostatic hazards
Sheets of paper stick together in industry
Wool, cotton and artificial fibres attract dust
Sparks produced in vehicles and planes

8. END of Electrostatics

9. Back to Basic Definitions 2 Electrostatics Click Back to
Matter is made up of tiny particles called atoms
Model of an atom :
nucleus
electron : negative (-) charge
proton : positive (+) charge
neutron : no charge
A proton has a positive charge and an electron has an equal negative charge while a neutron is uncharged

10. Back to Basic Definitions 2 Electrostatics Click Back to
Assume that we have a rod which is made of atoms and each atom contains 2 protons, 2 neutrons and 2 electrons
Electrically neutral (normal case)
protons
neutrons
electrons
20000
Positively charged
protons
neutrons
electrons
20000
18000
Negatively charged
protons
neutrons
electrons
20000
23000

11. Back to Basic Definitions 3 Electrostatics Click Back to
When a plastic rod is rubbed with a dry cloth, we have either one of the following cases.
flow of electrons
flow of electrons
Plastic rod : +ve charged
Cloth : -ve charged
Plastic rod : -ve charged
Cloth : +ve charged

12. Back to Basic Definitions 3 Electrostatics Click Back to
A charged (either +ve or -ve) rod can attract a piece of aluminium foil which is neutral initially.
flow of
electrons
Aluminium
flow
Since the electrons are attracted towards the upper end, the upper part becomes -ve while the lower part becomes +ve.
large attractive force
Since smaller separation means larger force, the attractive force is always larger than the repulsive force.
small repulsive force

13. Back to Ways of charging Electrostatics Click Back to
Extra high tension (EHT) power supply

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Van de Graaff generator

15. Ways of charging Electrostatics Next Slide
Consider two metal spheres which are supported by insulating stands as shown.
One of the sphere is negatively charged while the other one is uncharged.
Insulating stands
Negatively
charged sphere
Uncharged
sphere

16. Ways of charging Electrostatics Next Slide
They are brought into contact with each other.
Some of the electrons flow from the charged sphere to uncharged sphere.
flow of electrons
Both objects are then negatively charged.

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Both spheres are then separated and negatively charged.
This is called charging by sharing.

18. Ways of charging Electrostatics Next Slide
Consider two metal spheres which are supported by insulating stands as shown.
Both spheres are neutral and they are in contact with each other as shown.
Insulating stands
Uncharged
spheres

19. Ways of charging Electrostatics Next Slide
A positively charged rod is brought near one of the sphere.
Induced charge appears as electrons flow from one sphere to another.
Insulating stands
flow of electrons

20. Ways of charging Electrostatics Next Slide
The spheres are separated without removing the rod.
Insulating stands

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Then we remove the rod. One sphere is negatively charged while the other one is equally positive charged.
No loss of charge from the charged rod
This is the method of charging by induction and separation.
Insulating stands

22. Ways of charging Electrostatics Next Slide
We have a uncharged conducting sphere supported by insulating stand.
A positively charged rod is brought near the sphere.
Induced charge appears in the sphere.
Insulating stands
flow of electrons

23. Ways of charging Electrostatics Next Slide
Touch the sphere with your finger or collect the sphere to the earth with a conducting wire without removing the rod.
Electrons flow from the earth to the sphere and neutralize the +ve charge on the other side in the sphere.
Insulating stands
flow of electrons
earthing
process

24. Ways of charging Electrostatics Next Slide
Remove the finger or the wire without removing the rod.
Insulating stands

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Remove the rod and we get a negatively charged sphere.
No loss of charge in the rod is involved.
This is the method of charging by induction and earthing process.
Insulating stands

26. Back to Electric field Electrostatics Click Back to
The electric field pattern around a positive charge is shown.
The arrows and the lines represent the direction of force acting on a very small testing charge placed at that point.

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The electric field pattern around a negative charge is shown.
The arrows and the lines represent the direction of force acting on a very small testing charge placed at that point.

28. Electric field Electrostatics Next Slide
Various patterns are shown in the following figures:

29. Electric field
Electrostatics
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30. Electric field
Electrostatics
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Electric field
Electrostatics
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32. Applications 1 Electrostatics Next Slide
Action of a point : The charge has a tendency to concentrate on the sharp points of a conductor. Around these points, the electric field is so strong that the air molecules are ionized.

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Let’s take a negatively charged object with a sharp end as an example. Positive ions are attracted towards the point while negative ions are repelled.
Positive ions remove some electrons from the object and become neutral again. The charge on the object is reduced.
The negative ions are repelled and move away from the point. The stream of ion flow is called electric wind.
electric wind

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Lightning conductor is a metal rod with sharp ends and installed as shown in the following figure.
electric wind
Lightning conductor provides a route for electrons (lightning) to pass into the ground.
Electric wind reduces the charge on the cloud and the induced charge on the roof.