Electrical Interview Questions
1) What is Electrical Engineering?
Electrical Engineering is the field of Engineering that generally deals with
the study and application of electricity, electronics, and
electromagnetism.
2) What is electricity ?
Electricity is a general term used for all phenomena caused by electric
charge whether static or in motion.
3) What are the types of electricity ?
There are two types,(1) Static Electricity and (2) Current Electricity.
4) What is static electricity ?
Static electricity means electricity at rest in contradistinction to dynamic
or current electricity the effects of which are purely due to the
electrostatic field produced by the charge. As it is obtained by rubbing
two substance such as glass and silk it is also called frictional electricity.
5) What is current electricity ?
Current electricity means the electricity in motion the effects of which are
due to the flow of electrons in a conductor.
6) What are the types of current electricity ?
There are two types :- (1) Direct current and (2) Alternating current.
7) What are the different methods of producing electricity ? Give examples.
The methods are –
i) By means of frictions- Static electricity is produced.
ii) By means of chemical action in cells and batteries.
iii) By means of mechanical driving- Generator produces electricity in two
dissimilar methods.
iv) By means of heat – Thermal electricity is produced.
v) By means of lighting effect – Electricity is produced in photo electric
cell.
,8) Explain the difference between direct and alternating current?
Direct current (DC) is the flow of electric charge in only one direction. It is
the steady state of a constant-voltage circuit.
Alternating current (AC) is the flow of electric charge that periodically
reverses direction. If the source varies periodically, particularly sinusoidal,
the circuit is known as an alternating current circuit.
9) Where is D.C. used ?
(1)Battery charging, (2)Electroplating, (3)Electrolysis, (4) Relays, (5)
Traction motors, (6) Cinema projector.
10) Where is A.C. used ?
(1)House hold appliances, (2) Fan, (3) Refrigerators, (4)Power driving
motors. (5)Radio and T.V. Set etc.
11) What is active, reactive, apparent & complex power?
I) Active power: It is the actual power that is delivered to the load such
as transformer, induction motors, generators, etc and dissipated in the circuit. It is
denoted by P & its unit is watts W.
II) Reactive Power: The powers that continuously bounce back and forth between
source and load is known as reactive power. It is denoted by Q & its unit is VAR
voltage-ampere reactive.
III) Apparent Power: It is the product of voltage & current without referencing
the phase difference between them. It is a combination of active power & reactive
power. It is denoted by S & its unit Volt-Ampere, VA.
III) Complex power: it is the product of voltage & current with reference to
the phase difference between them. it is the complex sum or vector sum of the
active power & reactive power. It is denoted by S & measure in VAR.
12) What is a leading & lagging power factor & how can you improve it? State the
methods of power factor correction?
, The cosine of the angle between voltage & current is called the power
factor. If the current leads the voltage, it causes a leading power factor. If
the current lags voltage the power factor is lagging.
Most loads are inductive that causes a lagging power factor. Thus these
following methods are used for p.f correction (to nullify the lagging
current):-
i) Static Capacitor
The capacitor helps in providing a leading current that eliminates the lagging
component of current & improves the power factor
ii) Synchronous Condenser
It is an over-excited synchronous motor with no load that also provides a leading
power factor.
iii) Phase Advancer
Phase advancer is a simple AC exciter which is connected on the main shaft of the
motor and operates with the motor’s rotor circuit for power factor improvement.
Phase advancer is used to improve the power factor of induction motor in
industries.
13) Why do we improve the power factor?
The reason for improving the power factors are stated below;
Large Line Losses (Copper Losses): Line losses (I2R) depend on current. The
low power factor draws a large amount of current as compared to the high
power factor.
Large kVA rating and Size of Electrical Equipment: PF is inversely
proportional to KVA. Low PF equipment with a high KVA rating is larger in
size.
Large Conductor Size and Cost: we need large conductors to transmit the
heavy current required due to low power factor.
Poor Voltage Regulation and Large Voltage Drop: The large current due to
low PF causes a high voltage drop that needs to be regulated more often
than usual.
Low Efficiency: The losses due to the high current flow & voltage drop
deteriorate the efficiency of the system. The efficiency is maximum at PF=1.
14) What is a unilateral & bilateral circuit?
, A unilateral is a type of circuit whose properties change with the
direction of current flow or the voltage. The properties of a bilateral
circuit do not change with changing the current direction or supply
voltage.
15) What is a linear & non-linear circuit?
In a linear circuit, the relation between the current & voltage is linear i.e.
directly proportional. The circuit parameter such as frequency, resistance,
inductance, capacitance, etc. remains constant with varying current &
voltage.
While in the non-linear circuit, the current & voltage does not have a
linear relationship. The electrical parameters of such circuits changes with
varying voltage & current.
16) What could be the reason for the current to double in a linear circuit?***
There are two reasons for increasing the current:
1) Either the total resistance of the circuit is reduced by half
2) Or the supply voltage to the circuit is doubled.
17) Why is Battery Rating in Ah (Ampere hour) and not in VA or Watts?
A battery converts chemical energy into electrical energy which is the
charge stored inside the chemicals. The amount of current it can supply is
for a said time thus Ampere-hour Ah is the unit for its rating. While the
batteries supply direct current which has no phase or frequency thus there
is no concept of P.F or reactive power, thus no need for expressing it in VA
and its rated in Ah.
18) What is a primary & secondary cell?
The primary cell is a non-rechargeable battery that cannot be recharged
by any means. They are disposable & cannot be used once they are fully
discharged. They are mostly used in toys, handheld devices & remote
controllers, etc.
1) What is Electrical Engineering?
Electrical Engineering is the field of Engineering that generally deals with
the study and application of electricity, electronics, and
electromagnetism.
2) What is electricity ?
Electricity is a general term used for all phenomena caused by electric
charge whether static or in motion.
3) What are the types of electricity ?
There are two types,(1) Static Electricity and (2) Current Electricity.
4) What is static electricity ?
Static electricity means electricity at rest in contradistinction to dynamic
or current electricity the effects of which are purely due to the
electrostatic field produced by the charge. As it is obtained by rubbing
two substance such as glass and silk it is also called frictional electricity.
5) What is current electricity ?
Current electricity means the electricity in motion the effects of which are
due to the flow of electrons in a conductor.
6) What are the types of current electricity ?
There are two types :- (1) Direct current and (2) Alternating current.
7) What are the different methods of producing electricity ? Give examples.
The methods are –
i) By means of frictions- Static electricity is produced.
ii) By means of chemical action in cells and batteries.
iii) By means of mechanical driving- Generator produces electricity in two
dissimilar methods.
iv) By means of heat – Thermal electricity is produced.
v) By means of lighting effect – Electricity is produced in photo electric
cell.
,8) Explain the difference between direct and alternating current?
Direct current (DC) is the flow of electric charge in only one direction. It is
the steady state of a constant-voltage circuit.
Alternating current (AC) is the flow of electric charge that periodically
reverses direction. If the source varies periodically, particularly sinusoidal,
the circuit is known as an alternating current circuit.
9) Where is D.C. used ?
(1)Battery charging, (2)Electroplating, (3)Electrolysis, (4) Relays, (5)
Traction motors, (6) Cinema projector.
10) Where is A.C. used ?
(1)House hold appliances, (2) Fan, (3) Refrigerators, (4)Power driving
motors. (5)Radio and T.V. Set etc.
11) What is active, reactive, apparent & complex power?
I) Active power: It is the actual power that is delivered to the load such
as transformer, induction motors, generators, etc and dissipated in the circuit. It is
denoted by P & its unit is watts W.
II) Reactive Power: The powers that continuously bounce back and forth between
source and load is known as reactive power. It is denoted by Q & its unit is VAR
voltage-ampere reactive.
III) Apparent Power: It is the product of voltage & current without referencing
the phase difference between them. It is a combination of active power & reactive
power. It is denoted by S & its unit Volt-Ampere, VA.
III) Complex power: it is the product of voltage & current with reference to
the phase difference between them. it is the complex sum or vector sum of the
active power & reactive power. It is denoted by S & measure in VAR.
12) What is a leading & lagging power factor & how can you improve it? State the
methods of power factor correction?
, The cosine of the angle between voltage & current is called the power
factor. If the current leads the voltage, it causes a leading power factor. If
the current lags voltage the power factor is lagging.
Most loads are inductive that causes a lagging power factor. Thus these
following methods are used for p.f correction (to nullify the lagging
current):-
i) Static Capacitor
The capacitor helps in providing a leading current that eliminates the lagging
component of current & improves the power factor
ii) Synchronous Condenser
It is an over-excited synchronous motor with no load that also provides a leading
power factor.
iii) Phase Advancer
Phase advancer is a simple AC exciter which is connected on the main shaft of the
motor and operates with the motor’s rotor circuit for power factor improvement.
Phase advancer is used to improve the power factor of induction motor in
industries.
13) Why do we improve the power factor?
The reason for improving the power factors are stated below;
Large Line Losses (Copper Losses): Line losses (I2R) depend on current. The
low power factor draws a large amount of current as compared to the high
power factor.
Large kVA rating and Size of Electrical Equipment: PF is inversely
proportional to KVA. Low PF equipment with a high KVA rating is larger in
size.
Large Conductor Size and Cost: we need large conductors to transmit the
heavy current required due to low power factor.
Poor Voltage Regulation and Large Voltage Drop: The large current due to
low PF causes a high voltage drop that needs to be regulated more often
than usual.
Low Efficiency: The losses due to the high current flow & voltage drop
deteriorate the efficiency of the system. The efficiency is maximum at PF=1.
14) What is a unilateral & bilateral circuit?
, A unilateral is a type of circuit whose properties change with the
direction of current flow or the voltage. The properties of a bilateral
circuit do not change with changing the current direction or supply
voltage.
15) What is a linear & non-linear circuit?
In a linear circuit, the relation between the current & voltage is linear i.e.
directly proportional. The circuit parameter such as frequency, resistance,
inductance, capacitance, etc. remains constant with varying current &
voltage.
While in the non-linear circuit, the current & voltage does not have a
linear relationship. The electrical parameters of such circuits changes with
varying voltage & current.
16) What could be the reason for the current to double in a linear circuit?***
There are two reasons for increasing the current:
1) Either the total resistance of the circuit is reduced by half
2) Or the supply voltage to the circuit is doubled.
17) Why is Battery Rating in Ah (Ampere hour) and not in VA or Watts?
A battery converts chemical energy into electrical energy which is the
charge stored inside the chemicals. The amount of current it can supply is
for a said time thus Ampere-hour Ah is the unit for its rating. While the
batteries supply direct current which has no phase or frequency thus there
is no concept of P.F or reactive power, thus no need for expressing it in VA
and its rated in Ah.
18) What is a primary & secondary cell?
The primary cell is a non-rechargeable battery that cannot be recharged
by any means. They are disposable & cannot be used once they are fully
discharged. They are mostly used in toys, handheld devices & remote
controllers, etc.
