ELECTROSTATICS: Coulomb's law, Electric field & problems

1. UNIT II -ELECTROSTATICS
Coulomb's law,Electric
field & problems
Dr.K.G.SHANTHI
Professor/ECE
shanthiece@rmkcet.ac.in

2. ELECTROSTATICS
✘ Electric field, Coulomb's law, Gauss's law and applications,
Electric potential, Conductors in static electric field, Dielectrics
in static electric field, Electric flux density and dielectric
constant, Boundary conditions, Capacitance, Parallel, cylindrical
and spherical capacitors, Electrostatic energy, Poisson's and
Laplace's equations, Uniqueness of electrostatic solutions,
Current density and Ohm's law, Electromotive force and
Kirchhoff's voltage law, Equation of continuity and Kirchhoff's
current law
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3. ✘ An electrostatic field is produced by a static charge distribution.
✘ In electrostatics, electric charges (the sources) are at rest and
electric fields do not change with time.
✘ Positive and Negative charges are sources of an electric field.
✘ The devices used in solid-state electronics are based on
electrostatics.
✘ These include resistors, capacitors, and active devices such as
bipolar and field effect transistors, which are based on control of
electron motion by electrostatic fields.
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4. ✘ Almost all computer peripheral devices like Touch pads,
capacitance keyboards, cathode-ray tubes, liquid crystal displays,
and electrostatic printers are typical examples that are based on
electrostatic fields.
✘ In medical work, diagnosis is often carried out with the aid of
electrostatics, as incorporated in electrocardiograms,
electroencephalograms,
✘ In industry, electrostatics is applied in a variety of forms such as
paint spraying, electrodeposition, electrochemical machining, and
separation of fine particles.
✘ Electrostatics is used in agriculture to sort seeds, direct sprays to
plants, measure the moisture content of crops, spin cotton, and
speed baking of bread.
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5. COULOMB'S LAW:
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where Q1 and Q2 are the positive or negative
quantities of charge,
R is the separation, and
k is a proportionality constant.
If the International System of Units (SI) is used, Q is measured in
coulombs (C), R is in meters (m), and the force should be newtons (N).
Coulomb's law states that the force between any two point charges is:
 Directly proportional to the product Q1Q2 of the charges
 Inversely proportional to the square of the distance between them
 Is Directed along the line joining the charges.

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The constant of proportionality k is written as
Coulomb’s law is now

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Force acts along the line joining the two charges and is
repulsive if the charges are alike in sign or attractive if they are
of opposite sign.

8. PRINCIPLE OF SUPERPOSITION: 8

9. Problem
1. A 2 mC positive charge is located in vacuum at P1 (3, - 2, - 4)
and a 5 µC negative charge at P2 (1, - 4, 2).
a) Find the vector force on the negative charge.
b) What is the magnitude of the force on the charge at P1
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10. 10
The vector force on the negative charge:
The magnitude of the force on the charge at P1 :

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2.

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3.

13. ELECTRIC FIELD INTENSITY
✘ Consider one charge fixed in position, say Q1, and move a second charge
slowly around. There exists everywhere a force on this second charge. In
other words, this second charge is displaying the existence of a force field
that is associated with charge, Q1. This second charge a known as test
charge Qt . The force on it is given by Coulomb’s law,
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The electric field of a single point charge becomes:

15. Electric Field Intensity Due to n Point
Charges (Principle of Superposition):
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16. Electric Fields Due To Continuous
Charge Distributions
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Problem

19. THANK YOU
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