Electrical Electronics Engineering Question Bank

       CENTRAL INSTITUTE OF PLASTICS ENGINEERING & TECHNOLOGY

1 MARK—QUESTION

2 MARK ---QUESTION

3 MARK --- QUESTION

4/5 MARK ----QUESTION

COURSE : DPT 

SEMESTER: II 

SUBJECT : ELECTRICAL AND ELECTRONICS ENGINEERING

2 MARK—QUESTION

1. Define ohm’s law

Ans: Electric current is directly proportional to voltage and inversely proportional to resistance. 

V=IR;   V-Voltage, I-Current, R-Resistance

2. Define Current

Ans: The flow of charged particles through a conducting medium, such as wire. 

 Its unit is Ampere and denoted with letter A

3. Define Voltage

Ans: The potential difference between two points or two terminals. 

          Its unit is Volts and denoted with letter V

4. Explain the law of resistance.

Ans:i) It varies directly as its length

ii) It varies inversely as the cross section of the conductor

iii) It depends on the nature of the material

iv) It depends on the temperature of the conductor.

5. DefineKirchhoff’s current law

Ans:The sum of currents flowing towards a junction is equal to the sum of the currents flowing away from it.

6. DefineKirchhoff’s voltage law

Ans:In a closed circuit the sum of potential drops is equal to the sum of potential rises.

7. Define Time period

Ans: The time taken by an alternating quantity to complete one cycle is called time period (T)

8. Define frequency

Ans: The number of cycles per second is called the frequency of the alternating quantity.

f= PN/120

f- Frequency, P=Number of poles, N-Speed in r.p.m

9. Define cycle

Ans: One complete set of positive and negative values of an alternating quantity is known as cycle.

1 cycle= 360⁰ (or) 2π radians

10. Define Faraday’s law of electromagnetic induction

Ans: First law: When the magnetic flux is linked with a circuit an emf is induced in it.

Second law: The magnitude of the induced emf is equal to rate of change of flux linkages.

e =N(dΦ /dt)

11. Write the comparison of magnetic and electric circuit

Magnetic Circuit

The closed path for magnetic flux  is known as magnetic circuit

Flux=MMF/Reluctance

Permeance=1/Reluctance

Flux density=B=Φ/A,Wb/m2

Electric Circuit

The closed path for electric current is called electric circuit.

Current=EMF/Resistance

Conductance=1/Resistance

Current density=J=I/A, A/m2

12. Define DC Generator

Ans:An  electrical generator is a machine which converts mechanical energy into electric energy. It works on Fleming’s right hand rule.

13. Define Fleming’s right rule

Ans: The thumb represents the direction of the motion of the conductor relative to magnetic field. The fore finger represents the direction of magnetic field. The middle field represents the direction of the induced current.

14. What are the Constructional parts of DC generator.

Ans: Yoke, Pole core and Pole shoes, Armature coil, Armature windings, Commutator, Brushes,and Bearings.

15. Define torque

Ans: The turning or twisting moment of a force about an axis is called torque.

16. What is the role of commutator?

Ans:The function of commutator is to facilitate the collection of current from armature conductors. It converts the alternating current which is induced in the armature conductors into unidirectional current in the external load circuit.

17. Give some applications of DC motors?

Ans: Shunt motors: Lathes, Centrifugal pumps, Blowers and Fans etc.

Series motors: Electric locomotives, Trolley cars, Cranes and Hoists etc.

Compound motors: Elevators, Air compressors, Rolling mills etc.

18. Define transformers

Ans: Transformer is a static device that transfers electric energy from one circuit to another circuit. It does not change with frequency. It works on electromagnetic induction.

19. What is an ideal transformer?

Ans: An ideal transformer is one which gives output power exactly equal to the input power.

20. Write the characteristics of ideal transformer

Ans: i) It has no ohmic resistance

ii) It has no I 2 R losses

iii) It has no core losses

iv) It has no magnetic leakage.

21. What are the losses in Transformers, Explain? 

Ans: Iron loss: Iron loss occurs in the transformers Iron core due to hysteresis and eddy currents taking place. They are almost fixed irrespective of loading of transformers. 

Copper Losses: Copper losses are I2 R losses in the primary and the secondary windings of the transformer which with the loading of transformer.

22. What is Auto-transformer? 

Ans: In this transformer only one winding is used as primary and secondary. Also, primary and secondary are conductively coupled.

23. What is Buchholz relay? 

Ans: It protects the transformer from their internal faults like earth faults, winding short circuit, short circuit between phases, Puncture of bushing etc.

24. What is back EMF in DC motor? 

Ans: When the armature is rotated in a Magnetic field, then its conductors cut the lines of force and an EMF is induced in them. The induced EMF always opposes the applied EMF, hence it is called a back or counter EMF.

25. What is meant by earthed supply? 

Ans: A neutral point is not a good earth point unless it is not connected to earth. The conductor wire used for joining the neutral point to the earth electrode is called the earthed supply.

26. Define Electrical Earthing? 

Ans: The process of transferring the immediate discharge of the electrical energy directly to the earth by the help of the low resistance wire is known as the electrical earthing.

27. What is Fuse? 

Ans: Fuse is used to protect an electric circuit when the rated current exceeds in the circuit the fuse wire melts and opens the circuit.

28. What is meant by Lightning arrestors? 

Ans: A Lightning Arrestor is a device used in electrical power systems to protect the insulation on the system from the damaging effect of lightning.

29. Define Semiconductor materials? 

Ans: Materials having a conductivity of the order of somewhere between that of conductors and insulators are called semiconductors. Eg: Germanium and Silicon. 

30. What is an ideal diode? 

Ans: An ideal diode is a two terminal polarity sensitive device that has zero resistance when it is forward biased and infinite resistance when reverse biased.

31. What are the types of Transistors? 

Ans: Transistors are classified into three types: 

1. Bipolar Junction Transistors (BJTs) 

2. Field Effect Transistors (FETs) 

3. Insulated-Gate Bipolar Transistors (IGBTs) 

32. Explain about P-type and N-type semiconductors? 

Ans: P-type: A P-type material is one in which holes are majority carriers i.e. they are positively charged materials (++++) 

N-type: A N-type material is one in which electrons are majority charge carriers i.e. they are negatively charged materials (-----).

33. What are the common methods of Earthing? 

Ans: 1. Plate Earthing 

2. Pipe Earthing 

3.Rod Earthing 

4. Earthing through a water pipe

34. What isCorona?

Ans: The phenomenon of violet glow, hissing noise and production of ozone gas in an overhead transmission line is known as Corona.

35.Mention the two types of winding used in the DC machines? 

Ans: Lap winding used for low voltage, high current machine 

Wave winding used for high voltage, low current machine

36. Define MMF & Magnetic field intensity? 

Ans: MMF: The force that produces magnetic flux is called Magneto Motive Force(MMF) 

Magnetic field intensity: Force acting on a unit length of a conductor carrying unit current placed perpendicularly inside the magnetic field.

37. What is the SLIP? 

Ans: This difference between the speed of the rotor and speed of the rotating magnetic field in the stator is called slip.

38. What are advantages of leading power factor in distribution system? 

Ans: 1. Losses in the form of heat is reduced 

2. Cable becomes less bulky and easy to carry, and very cheap to afford 

3. It also reduces over heating of transformers.

39.What is a pn junction diode?

Ans:A p-n junction is an interface between two semiconductor material types, namely the p-type and the n-type, inside a semiconductor. The p-side or the positive side of the semiconductor has an excess of holes and the n-side or the negative side has an excess of electrons.

40. Define knee voltage of a diode. 

Ans:The forward voltage at which the current through the junction starts increasing rapidly, is called the knee voltage or cut-in voltage.

44.What is electric shock?

Ans: An electric shock is a dangerous and painful physiological effect caused by the passing of an electric current through the body.

45.What are the causes of electric shock?

Ans: i) Faulty appliances.

ii) Damaged or frayed cords or extension leads.

iii) Electrical appliances coming in contact with water.

iv) Incorrect or deteriorated household wiring.

v) Downed power lines.

vi) Lightning strike.

46.Define rectifier.

Ans: A rectifier is an electrical device composed of one or more diodes that converts alternating current (AC) to direct current (DC)

47.What are the types of rectifier?

Ans: i) Half wave rectifier

ii) Full wave rectifier

iii) Bridge rectifier

48.What is universal gates?

Ans: A universal gate is a gate which can implement any Boolean function without need to use any other gate type. The NAND and NOR gates are universal gates.

49. Write the truth table for NAND gate.

 

50. What is Skin effect? 

Ans: The tendency of alternating current to concentrate near the surface of a conductor is known as Skin Effect.