Electrical interview Questions contains interview question asked in interview
1. What is electric current?(units coulomb per second or Ampere)
Electric current
The controlled movement or drift of electrons through a substance is called the electric current.
Current may also be defined as the rate of net motion of an electric charge across a cross sectional boundary(as shown in fig).
A random motion of electrons in a metal doesn't constitute a unless there is a net transfer of charge with time i.e. electric current, i= Rate of transfer of electric charge
= dQ/dt
Coulomb is the practical as well as SI unit for measurement of electric charge charge. One coulomb is approximately equal to 624 x 10^16 electrons.
Since current is the rate of flow of electron through the conductor and coulomb is the unit of electric charge, the current may be specified in coulombs per second.
= dQ/dt
Coulomb is the practical as well as SI unit for measurement of electric charge charge. One coulomb is approximately equal to 624 x 10^16 electrons.
Since current is the rate of flow of electron through the conductor and coulomb is the unit of electric charge, the current may be specified in coulombs per second.
In practice the term coulomb per second is seldom used, a shorter term, ampere is used instead.
See the Below video tutorial for More details:
See the Below video tutorial for More details:
2. What is Resistance ? (units of resistance) (ohm definition)
Resistance(R)
Resistance may be defined as that property of a substance which opposes (or restricts) the flow of an electric current (or electrons) through it.
Units and ohm definition
The practical as well as mks (or SI) unit of resistance is ohm (Ω), which is defined as that resistance between two points of a conductor when a potential difference of one volt, applied between these points, produces in this conductor a current of one ampere, the conductor not being a source of any emf.
For insulators having high resistance , much bigger units kilo ohm or kΩ (10^3 ohm) are used. in case of very small resistances smaller units like milli ohm (10^-3) are employed.
Relation Between electric conductivity and resistance :
Electric Conductivity and Resistance are inversely proportional to each other. the reciprocal of resistance is called conductance.
Conductance = 1/R
For More Detailed Explanation see the below video.
Resistance may be defined as that property of a substance which opposes (or restricts) the flow of an electric current (or electrons) through it.
Units and ohm definition
The practical as well as mks (or SI) unit of resistance is ohm (Ω), which is defined as that resistance between two points of a conductor when a potential difference of one volt, applied between these points, produces in this conductor a current of one ampere, the conductor not being a source of any emf.
For insulators having high resistance , much bigger units kilo ohm or kΩ (10^3 ohm) are used. in case of very small resistances smaller units like milli ohm (10^-3) are employed.
Relation Between electric conductivity and resistance :
Electric Conductivity and Resistance are inversely proportional to each other. the reciprocal of resistance is called conductance.
Conductance = 1/R
For More Detailed Explanation see the below video.
Ohm's Law and It's limitations
Ohm's Law
The current flowing through the conductor is directly proportional to the voltage difference across the ends of the conductor and inversely proportional to the resistance.
The current flowing through the conductor is directly proportional to the voltage difference across the ends of the conductor and inversely proportional to the resistance.
This relation was discovered by Georg Simon Ohm and so it is known as Ohm's Law.
If 'I'current flowing through the conductor of resistance 'R' across which potential difference 'V' is applied then according to Ohm's law
Limitations
Ohm's Law cannot be applied to circuits consisting of electronic tubes or transistors because such elements are not bilateral i.e they behave in different way when the direction of flow of current reversed as in case of diode.
If 'I'current flowing through the conductor of resistance 'R' across which potential difference 'V' is applied then according to Ohm's law
Ohm's Law cannot be applied to circuits consisting of electronic tubes or transistors because such elements are not bilateral i.e they behave in different way when the direction of flow of current reversed as in case of diode.
Ohm's law also cannot be applied to circuits consisting of nonlinear elements like powdered carbon, thyrite, electric arc etc.
For More Explanation see the below video:
3. Laws of resistance (Resistivity ,specific resistance)
Laws of resistance
The resistance of a wire depends upon its length, area of cross section, type of material,purity and hardness of material of which it is made of and the operating temperature.
Resistance of a wire is
Directly proportional to its length, l i.e R α l
Inversely proportional to its area of cross section, a i.e Rα 1/a
Combining above two facts we have R α l/a
where ρ is a constant depending upon the nature of the material and is known as the specific resistance or resistivity of teh amterial of the wire.
Resistivity or specific resistance of amaterial may also be defined as the resistance of the material of unit length and unit cross section area.
The resistance of a wire depends upon its length, area of cross section, type of material,purity and hardness of material of which it is made of and the operating temperature.
Resistance of a wire is
Directly proportional to its length, l i.e R α l
Inversely proportional to its area of cross section, a i.e Rα 1/a
Combining above two facts we have R α l/a
where ρ is a constant depending upon the nature of the material and is known as the specific resistance or resistivity of teh amterial of the wire.
Resistivity or specific resistance of amaterial may also be defined as the resistance of the material of unit length and unit cross section area.
Specific resistance or resistivity of a material may also defined as the resistance of the material may also defined as the resistance between opposite faces of a unit cube of that material.
Resistivity is measured in ohm-metres Ω-m or ohms per meter cube
For More Details about Ohm's Law See the Video
4. What electrical value can be measured across the copper and zinc rods?
Voltage.
5. What is alternating current (AC)?
Alternating current changes direction. (50 Hz Supply)
6. What is Direct Current (DC)?
Does not change direction.
7. What does a fuse protect against in a circuit?
High current.
8. What unit is used to measure an electrical resistance?
Ohms.
9. What are the major parts of an electrical motor?
1. Motor enclosure
2. Stator
3. Rotor
4. Shaft
5. Bearings
6. End fan cover.
10. What is diffrent Electrical and Electronics Element?
Electrical elements deal with electricity while electronic elements deal with controlling the flow of electricity.
Electrical elements are passive components that do not control the flow of electricity.
Electronic elements are active components that control the flow of electricity.
Examples of electrical elements include resistors, capacitors, and inductors.
Examples of electronic elements include transistors, diodes, and integrated circuits.
11. What you do if motor stator core is short, what maintenance you do in HT panel, transformer maintenance, innovative modifications?
If motor stator core is short, maintenance in HT panel and transformer is necessary.
Isolate the affected equipment and de-energize it
Check the insulation resistance of the equipment
Identify the cause of the short circuit and repair or replace the affected parts
Perform regular maintenance on the HT panel and transformer to prevent future issues
Consider innovative modifications to improve the efficiency and reliability of the equipment
12. What is different SCR and thrisitor?
SCR stands for Silicon Controlled Rectifier.
SCR is a type of thyristor used for high power applications.
It is a type of thyristor used for high power applications.
SCR can handle high voltage and current levels.
It is commonly used in power control circuits, motor control circuits, and lighting dimmer circuits.
Thyristors are a family of semiconductor devices that include SCR, TRIAC, and DIAC.
13. What is tansformers working star delta stars?
Transformers work by transferring electrical energy from one circuit to another through electromagnetic induction.
Transformers consist of two coils of wire, a primary coil and a secondary coil, wrapped around a magnetic core.
When an alternating current flows through the primary coil, it creates a magnetic field that induces a voltage in the secondary coil.
The voltage in the secondary coil can be either higher or lower than the voltage in the primary coil, depending on the number of turns in each coil.
Transformers are used in power distribution systems to step up or step down voltage levels, and in electronic devices to isolate circuits and match impedances.