Basic Physics | Chapter Electricity

 Chapter Electricity

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Learning Objectives

1. Introduction
2. Electrical Nature of Matter
3. Insulators and Conductors
4. Electric Field
5. Electrostatic Induction
6. Electrostatic Potential
7. Capacitor
8. Electromotive Force (E.M.F)
9. Electric Cells
10. Electric Current
11. Electric Circuit and Combination of Resistances
12. Direct Current and Alternating Current
13. Electrical Energy and Joule’s Law
14. House Circuits.

Electrical Nature of Matter:

It is a fact that matter is made up of electron, proton and neutron. The electron has a negative charge equal to 1.6 x 10^-19 coulomb and a proton has a positive charge of same value and neutron is neutral in charge. As matter has charge of electricity, this fact is called electrical nature of matter.

Definition of Insulators:

A substance that is poor conductor of electricity and heat is called insulator. Both properties usually occur as a consequence of a lack of mobile electrons which are free to move but insulator has no free electrons. So they cannot conduct electricity and heat. Example: Wood, Rubber etc.

Definition of Conductors:

The substance which are good conductors of heat and electricity are called conductors. Both these properties usually occur of a lack of mobile electrons which are free to move and a conductor has a lot of free electrons so they conduct electricity easily. Example: Silver, Copper, Iron, Gold, etc.

Colums’s Law:

Statement of coulombs law: The power of fascination or repugnance between two point charges is straightforwardly corresponding to the result of the charges and contrarily relative to the square of the distance between them.

Derivation of expression of coulomb’s law or mathematical form of coulomb’s law:

Consider two point charge q₁ and q₂ are positioned at a distance of r₁ then the force ‘F’ of attraction or repulsion between them is

What is unit of K?

Where ‘K’ is constant of proportionality whose value in S.I unit is.

K = 8.9990 x 10⁹  =  9 x 10⁹

K = Nm²C ^-2

And the K is commonly expressed in terms of another constant Є (epsilon) 

Define Permittivity of free space OR Absolute Permittivity and its unit:

We know the force between two charges depends on the nature of medium placed between the charges. The absolute permittivity of medium is the ratio of electric displacement to the straight of the electric field at the same point. The absolute permittivity of free space is Є_o

Є_o = 8.854184 x 10^-12N^-1m^-2C ^-2.

Define Relative Permittivity and its unit:

The dielectric constant of a medium is known as relative permittivity and it is defined as the ratio of forces between two charges placed in the air or vacuum to the force when they are placed in the medium. It is denoted by Є_r.

Force of attraction:

If the changes are different in nature i.e one is positive and another us negative then the forces between them is attractive.

Force of repulsion:

If the charges are same i.e. both are negative or both are positive then the force between them is repulsive.

Factors on which forces depend:

As we know the formula of force is

Then the force is directly proportional to q₁ and q₂, and inversely proportional to the square of their distance and ‘Є’.

Unit of charges

The unit of charges in S.I units is coulomb (C). One coulomb of charge being the quantity of charge which when placed one meter from an identical charge in vacuum repels it with a force of 8.99 x 10⁹N.

Some multiple:

1C = 103mC	1C = 10-6MC
1C = 106µC	106C = MC
1C = 109nC etc.

 

Electric Field

Electric field is defined as a region around a charged body where its effect can be found. This effect is detected by means of another charge so the relative definition is as follows. “Electric field is defined as a region around a charged body where another charged body experiences an electric force when placed at any point in the field”. Existence of electric field is proved by bringing a test charge into the field.

Further Topics will be update soon

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Reference: taken from a book which is written by: M.R. Warsi & Sohail Ahmed

These notes will be helpful for all kind of tests like JEST, SST, PST, ECT, SPSC, CSS, PMS, etc.