Basic Electrical Interview question

1.What is static electricity?

Static electricity means electricity at rest. If we join a charged conductor to another conductor, electricity flows from one to the other. This way an electric current is produced, which lasts for a moment only. Static electricity is no use. Rubbing of two different materials having different electrons produces this.

2. What is current?

Flow of electrons in any conductor is called electric current. Its symbol is ‘I’ and measuring unit is Ampere measured by ammeter or ampere meter.

3. What is electro-motive force (emf) or voltage?

It is the pressure that moves the electrons to flow in any conductor. It is also known as electromotive force voltage. Its symbol is ‘E’ or ‘V’ and measuring unit is volt measured by voltmeter.

4. What is potential difference (P.D)?

The difference of potential between two points in a circuit is the voltage required to drive the current between them or the voltage drop between those two points is called the potential difference. P.D = R * I volts.

5. What is terminal voltage (VT)?

It is the voltage available at the terminal of the source of supply. It’s symbol is VT. VT = emf – P.D ‘

6. What is resistance?

Resistance is the property of a substance, which gives opposition to flow of electrons through itself. Its measuring unit is ohm and measured by ohmmeter, multi meter, wheat stone bridge, and post office box. There are two types of resistances and they are fixed resistance and variable resistance.

7. What is ampere?

The international ampere is defined as that steady current which, flowing through a solution of silver nitrate, deposits silver at the rate of 0.001118 gm/sec.

8. What is volt?

The international volt is defined as 1/1.0183 of the emf of a Weston cadmium cell. It is that difference of potential which, when applied to a conductor whose resistance is 1 (one) international ohm, will cause a current of 1 (one) international ampere to flow.

9. What is matter?

The matter is defined as anything, which possesses weight and occupies space and can be in any of three forms solid, liquid or gaseous. The matter consists of three ingredients, which are protons, neutrons and electrons.

What is the speed of electricity or electrons? The speed of electricity or electrons is 297842 km (186000 miles) per second.

11. How we get electric shock?

On all alternators, transformers neutral is earthed. Human body is conductor and when touched to the live conductor it completes its shortest root though the body and the body gets electric shock in which its nervous system, the heart, respiratory system may cease to function.

12. What is fuse and what materials used for fuse wire?

Fuse is a weakest point in an electrical circuit, which melts when the excess current flows through it in the electrical circuit. The materials, which can be used in fuses, are tin, lead, zinc, silver, antimony, copper, and aluminium, etc.

13. What is fusing factor?

The ratio of minimum fusing current and the current rating of fusing element is called the fusing factor. Fusing factor = minimum fusing current / current rating of fusing element. Its value is always more than 1 (one).

14. What is soldering and what is brazing?

Soldering is the process of joining two metals with an alloy whose melting point is less that of the materials to be soldered. Soldering at high temperature using brass as solder is called brazing or hard soldering. The composition of the fine solder (soft solder) is tin 60% and lead 40%. Its melting point is 190°C and is widely used.

15. What are the sources of electricity?
16. Battery (chemical source) b. Generator (magnetism) c. Thermocouple (heat generated) d. Light (photo electric or solar cell) e. Pressure (piezo electricity) f. Friction (static electricity)
17. What is conductance?

Conductance is the property of the conductor, which allows the flow of electric current through it. Conductance is denoted by the letter G and is reciprocal of resistance. The unit of conductance is mho. A substance, which posses conductance as its major property can be called as a good conductor.

17. What you mean by insulator?

A substance, which will not allow the flow of electric current to pass through it is called the insulator. The conductance and conductivity is zero in insulators. Insulators are used to isolate the electric current from neighbouring parts. Insulators will not allow the leakage of current, short-circuiting current, shock to the operator and isolates the electric current safely with out any diversion to any other place.

18. What is electrode?

A conducting element used for converging (centering) current to and from a medium is called electrode. There are two types of electrode. A positive and other is negative.

19. What is the difference between resistor, rheostat and potential divider?

Resistor: a fixed resistance connected permanently in the circuit for limiting the current to definite value is called the resistor. Rheostat: a variable resistance by sliding contacts on it the current can be varied is called rheostat. Potential divider: when a resistance is used to develop a voltage drop it is called a potential divider.

20. What is flux?

Flux is a cleanser and is used to remove and prevent oxidation of the metals, allowing the solder to flow from and to, to unite the solder more firmly with the surface to be joined.

21. What is skin effect?

Electricity has affinity (fondness) to pass through peripheral surface of the conductor. This effect of electricity flowing through the peripheral surface of the conductor is known as skin effect. 45. What are the advantages of stranded cables? a. It gives flexibility. b. It prevents skin effect. c. Increases current carrying capacity. d. It provides easy in soldering joint. e. If one strand breaks the other will carry the load current.

22. What is capacitor? On what factor capacity of a capacitor depends?

Capacitor or condenser is a device to store electrical energy and to release it into the circuit of which the capacitor forms a part. Capacity of a capacitor depends on following factors a. Capacity of the capacitor is directly proportional to the area of the plate. b. Capacity is inversely proportional to the distance between the plate. That is if the distance is more the capacity decreases or if the distance is less the capacity more. c. It depends on the nature of dielectric constant.

23. On what factor voltage rating of the capacitor depend?

The voltage rating of the capacitor depends on the distance between the plates of the capacitor. If the voltage exceeds, the electrons across the space between the plates can result in permanent damage to the capacitor.

24. What are the types of capacitor?
25. Paper capacitor. b. Rolled plastic cover or polyester type capacitor. c. Mica capacitor. d. Silver mica capacitor. e. Ceramic capacitor. f. Electrolytic capacitor.
26. What is the resultant capacitance in series and parallel circuit?

In series circuit the resultant capacitance 1/CT = 1/c1+1/c2 + 1/cn farad. In parallel circuit the resultant capacitance CT = c1 + c2 + cn farad.

26. What is work?

Work is said to be done, when the point of application of the force moves. Work done is equal to force * distance. The unit of work is Newton (M.K.S system) and joule (1 Newton Meter).

27. What is power?

Power is the rate of doing work or power is the work done per second. Power = Work / time. Unit of electrical power is watt. One mechanical horsepower is equal to 746 watts (British) and 735.5 watts (metric) or 735.5 joules/sec. So 1 kW is equal to 1.34 horsepower (British) and 1.36 horsepower (metric).

28. What is energy?

Energy is the capacity to do the work. The unit of energy is joule or watt-second or watt-hour or kilo watt-hour.

29. Define Joule’s law.

The heat generated in conductor (resistance) while the flow of current is directly proportional to the square of the current, the resistance of the conductor and time for which the current flows. H = I2 R t/J calories. Where J is mechanical equivalent of heat is equal to 4.2 Joules. In electricity H = 0.24 I2 R t calories.

30. What is electrolysis?

When current passes through an acid or a salt, it de-composes and the two decomposed portions tend to move in opposite direction. This process is called the electrolysis. Or the process of decomposing a liquid by the passage of electric current (DC) through it is called the electrolysis or electric analysis.

31. State the faraday’s laws of electro magnetic induction.

In 1831 Faraday discovered the production of electric current in electric conductor by converting magnetism. Faraday has mentioned two laws known as faraday’s laws of electro magnetic induction. First law- Whenever a conductor causes to cut the magnetic lines of force an emf will be induced in that conductor. Second law-The quantity of electricity or the value of the emf produced in that conductor is directly proportional to the rate of change of flux linked with that conductor.

32. How we can find the direction of induced emf?

The direction of induced emf can be find out by the ‘Fleming’s right hand rule’, and ‘lenz’s law’

Fleming’s right hand rule-Fleming’s right hand rule states that, if one extends the thumb, fore finger and middle finger of the right hand at right angle to each other in such a way that the thumb point in direction of motion of the conductor, the fore finger in the direction of flux (from north to south pole), then the middle finger is indicate the direction of the induced emf in the conductor.

Lenz’s law- The lenz’s law states that, electro magnetically induced current always flows in such a way or direction that the action of magnetic field set up by induced current tends to opposes the root cause which produces it.

33. What is eddy current?

Eddy currents are those which are produced or induced in the mass of metal whenever the metal are moved in magnetic field of the magnetic field is moved across the mass metal so as to link it. The direction of this eddy current is always in opposite direction to the cause to produce them as per lenz’s law.

34. Explain Kirchhoff’s laws.

Kirchhoff’s laws are used in complex network circuits to determine the equivalent total resistance and the current flowing in various conductors of that circuit. Mainly there are two laws. a. Point law or current law. b. Mesh law or voltage law.

Point law or current law. The point law states that, the algebraic sum of the currents meeting at any point or junction or node of a network is zero. In other words the sum of the currents flowing towards the junction or node or any point of network is equal to the total current flowing away from that junction.

Mesh law or voltage law. The mesh law states that, in any closed electrical circuit the algebraic sum of the potential drops is equal to the sum of the impressed emf’s acting in that close circuit. In this the important factor is to determine the emf sign to calculate the total emf.

35. What are the testing of wiring installation?

Following are the tests to be done after installation of wiring. a. Polarity test. b. Short circuit test. c. Continuity test. d. Insulation test between conductors and conductors to the earth. e. Earth continuity test.

36. What are the advantages of AC over DC?
37. For the same capacity alternators are cheaper than DC generators, because alternator is not having commutator arrangement and there by small in size. b. Alternating current produces pulsating magnetic field and there by it posses the property of inductance and capacitance. c. Alternating current can be step-up or step-down by static transformer. d. AC can be transmitted with very less cost in comparing to DC transmission. e. Alternating line losses are very less comparing to DC line losses. f. An alternators and AC motor requires very less maintenance. g. Charge per unit for AC is less than DC.
38. Define AC.

Alternating current is that type of electric current, which changes it’s magnitude and direction periodically.