FUNDAMENTALS

ELECTROSTATICS:


All bodies are able to take a charge of electricity, and this is known as

static electricity. The charge on the body is measured by means of

the force between the two charges, this force following the inverse square law

( i.e ) the force is proportional to the product of the charges and inversely

Proportional to the square of the distance between them).

This may be written as F=q1q2/4╥ﻉ○d² N

Where q1 and q2 are the charges in coulombs and d the distance in metres- the

Space in between the charges being either air or a vacuum with permittivity ﻉ○.

N is Newtons.

If the two charged bodies are separated by some other medium the force acting

may be different, depending upon the relative permittivity of the dielectric

between the two charged bodies.

The relative permittivity is termed as dielectric constant.

In this case force F= q1q2/ 4╥ﻉŗﻉ○ d² N

whereﻉŗ is the constant for the particular dielectric. For Air or Vacuum the value

ofﻉŕ s Unity..

FUNDAMENTALS& BASIC THOERY

POWER:



Power is defined as the rate of doing work. The electrical unit of power (P) is the Watt(W). With steady current as with d.c



1W= 1Vx1A



or W=VA



in symbols P = VxI. 1KW= 1000Watts.







ENERGY:



Energy is defined as powerxTime



(i.e) Electrical energy = VIt, where t is time in seconds. The unit is joules which is equivelent to 1 ampere at 1 volt for 1 second.



The practical unit of Energy is the kilowatt hour .



Kwh= watts x hours/1000



Energy loss in Resistance:



If current ' I ' is passedthrough resistance 'R'nthen the voltage drop across the resistance will be



V=IR



The watts used wil lbe VI, Therefore, the power in the circuit will be


P=VI=(IR) x I =I²R

I²R is usually known as the copper loss or the I²R loss.

FUNDAMENTALS

FUNDAMENTALS

CURRENT:

The rate at which Electricity flows is termed as "CURRENT". The magnitude of the current deponds upon the electromotive force and also depends upon the nature and dimensions of the path through which it circulates, The steady flow of current is given by the quantity of electricity which passes a given point in one second.

OHM'S LAW:

Ohm's law states that the current in a d.c circuit varies in direct proportion to the voltage and is inversly proportional to the ressistance of the circuit.

(i.e) Current=Electromotive force/resistance

where the units for the above quqntities are ,

current - The Ampere (A)

Electromotive force- the Volt ( V)

Resistance-the Ohm (R)

Ohm's law can be written as, I = V/R or V=I x R

RESISTIVITY:

THe Resistivity of any material is the resitance of a piece of material having unit length and unit sectional area. The symbol is p and the unit is ohm metre. The resistivity of material is not constant but depends on the temperature.

Resistance of a conductor:

The resistance of a uniform conductor with sectional area A and length l is given by,

R = p l /A

The units used must be in millimeters and square millimeters if p is in ohm millimeter units.