Electrical Circuit Theorems for Circuit Analysis

Electrical Circuit Theorems:

To solve problems in electrical networks, there are number circuit theorems have been developed like
(1) Kirchhoff's laws
(2) Superposition theorem
(3) Thevenin theorem
(4) Norton Theorem
(5) The maximum power transfer theorem

In this post we have listed all these theorems. We believe that this post will serve as a ready reference for you.

Kirchhoff's laws:
(a) Current Law:
 At any junction in an electric circuit the total current flowing towards that junction is equal to the total current flowing away from the junction, i.e. I =0

(b) Voltage Law:
 In any closed loop in a network, the algebraic sum of the voltage drops (i.e.products of current and resistance) taken around the loop is equal to the resultant e.m.f. acting in that loop.

Superposition Theorem:
In any network made up of linear resistances and containing more than one source of EMF, the resultant current flowing in any branch is the algebraic sum of the currents that would flow in that branch if each source was considered separately, all other sources being replaced at that time by their respective internal resistances.

Thevenin Theorem:
The current in any branch of a network is that which would result if an EMF. equal to the potential differential across a break made in the branch, were introduced into the branch, all other EMFs being removed and represented by the internal resistances of the sources.

Norton Theorem:
The current that flows in any branch of a network is the same as that which would flow in the branch if it were connected across a source of electrical energy, the short-circuit current of which is equal to the current that would flow in a short-circuit across the branch, and the internal resistance of which is equal to the resistance which appears across the open-circuited branch terminals.

The Maximum Power Transfer Theorem:
The power transferred from a supply source to a load is at its maximum when the resistance of the load is equal to the internal resistance of the source

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Basic Electrical Engineering Interview Questions Answers 1

Basic Electrical Engineering Interview Questions Answers 1

[Q] Define Power and Energy?
The rate at which work is done in an electric circuit is known as Electric power.
Power = Voltage X Current
The basic unit for electric power is Watts
The instrument used to measure the power is known as watt meter.

The total amount of work done in an electric circuit is called as electric energy. 
Energy = Power X Time
the basic unit is Joule or watt-sec
The practical unit is Kilo watt-hour
The instrument used to measure the energy is known as Energy meter.

[ Like this you have to explain elaborately in the interviews. The interviewer will expect detailed answer from the candidate.
If he feels that you are deviating too much, then he will stop you and ask another question. Please don't answer in one line. Add related points
where ever possible]

[Q] In our house are we monitoring/measuring power or energy?
Energy. It is done by energy meter.

[Q] what is meant by cycle in ac waveform? what is period? Define frequency?
One complete set of change in value is known as waveform.
If you any basic question on AC waveform, then first draw an ac waveform and explain with reference to the waveform.

[Q] Explain about various AC Values?
Instantaneous value:
Instantaneous values are the values of the alternating quantities at any instant of time. They are represented by small letters like i, e etc.
Peak value:
The largest value reached in a half cycle is called the peak value or the maximum value or the amplitude of the waveform. Such values are represented by Vm, Im etc.
Peak-to-peak value is the difference between the maximum and minimum values in a cycle.
Average value:
The average or mean value of a symmetrical alternating quantity (such as a sine wave), is the average value measured over a half cycle (since over a complete cycle the average value is zero). For a sine wave, average value = 0.637 times maximum value 
RMS Value: 
The effective value of an alternating current is that current which will produce the same heating effect as an equivalent direct current. The effective value is called the root mean square (rms) value and whenever an alternating quantity is given, it is assumed to be the rms value.

[Q] What is form factor and peak factor?
The ratio of rms value to average value of an ac quantity is called form factor.
Form Factor = RMS value/ Average value
The ratio of maximum value to the RMS value of an ac quantity is called as peak factor.
Peak Factor = Maximum Value/RMS value