Basic Electrical and Electronics Engineering Principles

   1.2 Charge
The unit of charge is the coulomb (C)where one
coulomb is one ampere second. (1coulomb=6.24×
1018 electrons).The coulomb is defined as the quantity
of electricity which flows past a given point in an electric circuit when a current of one ampere is maintained
for one second. Thus,
charge, in coulombs Q=It
where I is the current in amperes and t is the time in
seconds.

1.3 Force
The unit of force is the newton(N) where one newton
is one kilogram metre per second squared. The newton
is defined as the force which, when applied to a mass of
one kilogram, gives it an acceleration of one metre per
second squared. Thus,
force, in newtons F=ma
where m is the mass in kilograms and a is the acceleration in metres per second squared. Gravitational force, or weight, is mg, where g=9.81m/s2.

1.4 Work
The unit of work or energy is the joule(J) where one
joule is one newton-metre The joule is defined as the work done or energy transferred when a force of one newton is exerted through a distance of one metre in the direction of the force. Thus work one on a body, in joules, W=Fs
where F is the force in newtons and s is the distance in metres moved by the body in the direction of the force.
Energy is the capacity for doing work.

1.5 Power
The unit of power is the watt(W) where one watt is one
joule per second. Power is defined as the rate of doing work or transferring energy. Thus, power, in watts, P=W/t
where W is the work done or energy transferred, in
joules, and t is the time, in seconds. Thus,
energy, in joules, W=Pt

1.6 Electrical potential and e.m.f.

The unit of electric potential is the volt(V), where one
volt is one joule per coulomb. One volt is defined as
the difference in potential between two points in a conductor which, when carrying a current of one ampere, dissipates a power of one watt, i.e.
volts= watts
amperes = joules/second
amperes
= joules
ampere seconds = joules
coulombs
A change in electric potential between two points in
an electric circuit is called a potential difference. The
electromotive force (e.m.f.) provided by a source of
energy such as a battery or a generator is measured in
volts

1.7 Resistance and conductance
The unit of electric resistance is the ohm, where one ohm is one volt per ampere. It is defined as the resistance between two points in a conductor when a constant electric potential of one volt applied at the
two points produces a current flow of one ampere in the conductor. Thus,
resistance,inohms R=V/I

where V is the potential difference across the two points,
in volts, and I is the current flowing between the two
points, in amperes.
The reciprocal of resistance is called conductance
and is measured in siemens(S).Thus
conductance, in siemens G=1
R
where R is the resistance in ohms.

1.8 Electrical power and energy
When a direct current of I amperes is flowing in an
electric circuit and the voltage across the circuit is
V volts, then
power, in watts P=VI
Electrical energy=Power ×time
=VIt joules
Although the unit of energy is the joule, when dealing with large amounts of energy, the unit used is the
kilowatt hour(kWh)where
1kWh=1000 watt hour
=1000×3600 watt seconds or joules
=3600000J

1.9 Summary of terms,units and their symbols

Quantity     Quantity Symbol  Unit         Unit Symbol
Length            l                            metre           m
Mass              m                          kilogram       kg
Time               t                            second          s
Velocity          v                           metres per     m/s or
                                                     second           ms−1
Acceleration   a                           metres per      m/s2or
                                                      second           ms−2
                                                        squared
Force               F                           newton             N
Electrical         Q                           coulomb           C
chargeor
quantity
Electriccurrent   I                            ampere            A
Resistance          R                            ohm
Conductance      G                            siemen           S
Electromotive      E                           volt                 V
force
Potential              V                           volt                 V
difference
Work                    W                           joule              J
Energy                E(orW)                     joule              J
Power                 P                             watt               W