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Fundamentals of Electrical

Engineering

Lecture 2

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Recap

Electrical Engineering

Charge & electric charge

Force Work

Power

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Revision

Atomic model

Free electrons

Ions Conductors, insulators and semi-conductors

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Potential Difference

When charges are detached from one bodyand transferred to another,potentialdifference or voltage results between them.

The unit of electric potential is volt (V) whereone volt is one joule per coulomb.

=

Here W is energy in joules, Q is charge incoulombs and V is resulting voltage in volts.

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Potential Difference (cont.)

One volt is defined as the potential differencein potential between two points in theconductor which, when carrying a current of

one ampere, dissipates a power of one watt.

=

=

A change in electric potential between twopoints in an electric circuit is calledpotentialdifference.

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Electromotive force

EMFrefers to voltage generated by a battery

or by magnetic force according to Faraday's

Law, which states that a time varying magnetic

field will induce an electric current.

Electromotive "force" is not considered a

force, as force is measured in newtons, but a

potential, or energy per unit of charge,measured in volts.

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Current

Some elements like copper have free

electrons.

These electrons move randomly throughout

the material, but their net movement in any

given direction is zero.

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Current (cont.)

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This movement of electrons is called current

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Current (cont.)

Current is measured in amperes.

=

Here I is current in amperes, Q is charge incoulomb and tis time in seconds.

One ampere is the current in a circuit when onecoulomb of charge passes a given point in one

second. Note: tdoes not represent a discrete point in

time but is the interval of time during which thetransfer of charge occurs.

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Example

If 840 coulombs of charge pass through the

imaginary plane during a time interval of 2

minutes, what is the current?

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Current Direction

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Alternating Current

Current that changes direction cyclically i.e.

charges alternately flow in one direction, then

in other in a circuit.

Most common example is AC power system

that supplies energy to your home.

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