# Common Interview Questions for Electrical Engineering Polytechnic Students

## 1). Explain Ohm’s Law.

According to Ohm’s Law, current is directly proportional to the volts and inversely proportional to the ohms between two points. The degree of insulation can be mathematically defined as

V=IR,

where

V - Voltage,

I - Current, and

R - Resistance.

## 2). What is a transformer and how do they function?

A transformer is an electrical device that is utilized to transform the voltage of an AC use. It follows the working of the electromagnetic induction theory. When an a. c. is passed through the primary coil it produces a magnetic field that produces voltage in the secondary coil, either transforming the voltage to higher or lower value.

## 3). Explain the difference between AC and DC.

AC which stands for Alternating Current is that type of current in which the flow of electrons changes its direction periodically or in cycles.

DC or Direct Current is a form of current which has the continuous movement of charges in a definite direction.

## 4). In electrical engineering, what are the types of motors used?

• DC Motors: Applied in occasions where it is obligatory to maintain adjustable speed.
• AC Motors: Induction motors & Synchronous Motors are part of this category which are popular in the industrial environment.
• Stepper Motors: Used is very specific control systems that require accurate control such as robotics.
• Servo Motors: Mainly adapted in applications that need accurate position adjustment of the angular position as in CNC.

## 5). What is diode and what does it do?

A diode is a passive device which is made of semiconductor material and it permits current flow in only one direction. It is applied in rectification (direct conversion of AC to DC), demodulation of signals, and as shielding in circuits.

## 6). What is Power Factor?

Power Factor is the actual power with regard to watt used into doing work in the circuit while the apparent power with regard to volt-amperes flowing inside the circuit. It is the ratio of the actual load to the maximum load that can be supplied to a circuit at any given time. A power factor of 1 means that maximum power is used; a power factor below 1 means there is wasted power.

## 7). How are circuit breakers classified?

MCB (Miniature Circuit Breaker): Employed in low power applications.

MCCB (Molded Case Circuit Breaker): Used in circuits to supply higher voltages.

RCCB (Residual Current Circuit Breaker): Applied in discouraging electric shocks.

ACB (Air Circuit Breaker): Applicable in industrial usage for voltages that are high.

## 8). Can you explain the difference between a fuse and a circuit breaker?

A fuse on the other hand is a circuit protection gadget that is utilized once and melts when higher than appropriate current is passed through it to break the circuit. A circuit breaker on the other hand is a reusable switch that disconnects the circuit when there is an overload or short circuit and then can be reused.

## 9). State Kirchhoff’s Current Law (KCL).

Kirchhoff’s current law is formally established by the following statement: the sum of currents that flow in a closed circuit is equal to the sum of currents of the same circuit at any junction where they meet.

## 10). What are the benefits of using a three-phase system instead of the single-phase system?

A three-phase system is superior to a single-phase system of transmitting and distributing electrical power because it:

• Delivers a constant amount of power to the load most of the time.
• Its conductor material requirements are lower for the equivalent power.
• This will allow for results in less power loss.

## 11). What is an Inductor, and what for it is used in a circuit?

An inductor is an electrical device made up of a coil which stores energy in the form of a magnetic field when it is through by current. It opposes changes in current and is most often used in filters and transformers and any inductive load.

## 12). What is a relay, and where is it used?

A relay is an electric switch that uses electromechanical or electronic means to open and close circuit. It is applied in operations such as switching high power devices with low power signals, use in motor starters and use in protection circuits.

## 13). What is the working principle of an induction motor?

An induction motor depends on the stator’s created rotating magnetic field to interact with the current created in the rotor so as to generate the required torque that will cause rotation of the rotor.

## 14). What are the various classifications of electrical cables?

Electrical cables are usually classified under their use and by their formation and some of the electrical cables include:

• PVC (Polyvinyl Chloride) Insulated Cables: For general wiring purposes, this type wire is employed.
• XLPE (Cross-linked Polyethylene) Cables: Commonly employed where high voltage work is being conducted.
• Armored Cables: Employed in cable protection in underground applications.
• Flexible Cables: Applied in products that has to bend and flex.

## 15). What is a capacitor and how does it work in a circuit?

A capacitor is a passive circuit element that is capable to store electrical charge in a dielectric field between the plates. It offers deftly consisting direct current (DC) but allows the alternating current (AC) to pass through. They are used in the circuits as the filter, energy storage device as well as in power conditioning circuits.