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Electrical interview Questions 1 contains interview question asked in interview

1. What is electric current? (Units coulomb per second or Ampere)
2. What is Resistance? (Units of resistance) (Ohm definition)
3. Laws of resistance (Resistivity, specific resistance)
4. What electrical value can be measured across the copper and zinc rods?
5. What is alternating current (AC)?
6. What is Direct Current (DC)?
7. What does a fuse protect against in a circuit?
8. What unit is used to measure an electrical resistance?
9.  What are the major parts of an electrical motor?

### 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.

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:

### 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.

#### 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.

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.

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.

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

Voltage.

### 5. What is alternating current (AC)?

Alternating current changes direction. (50 Hz Supply)

### 6. What is Direct Current (DC)?

Does not change direction.

High current.

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.