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Basic Electrical interview Questions & Answers paper-3

41. What fundamental relation does ohm’s law express ?

Ans : Ohm’s law gives the relation among the voltage, current and resistance in a circuit and expressed by the equation, I = V/R .

42. State three equations of Ohm’s law.

Ans : I = E/R, R = E/I, and E =I.R. Where I is the current flow in amperes, R is the resistance in ohms and E is the E.M.F. in volts.

43. Can you apply ohm’s law to all types of electrical conductor ?

Ans: No. Ohm’s law can be applied only in the cases of conductor through metals and in electrolytic conduction. It can not be applied in the cases of conduction through ionized gases or semiconductors.

44. A bulb is connected to a battery of F.M.F. 10V and the current is found to be 0.01 A. When the bulb is connected to 220V mains, the steady current is 0.05A. Explain this apparent disagreement with ohm’s law.

Ans: It is due to the difference in temperature of the filament of the bulb in the two cases. The temperature of the filament is more when the bulb is connected to 220V main and thus the resistance also increases. Hence we have the deviation from the law.

45. What are the limitations of Ohm’s law ?

Ans : Ohm’s law is not applicable to non ohmic conductors like vacuum tubes, discharge tubes and semiconductors.

46. What is an electric circuit ? What are its types ?

Ans : Electric circuit is a complete traversed path for the flow of electric current which consists of source of supply, connecting wires, switches and load resistances. There are three types of circuit, (a) Closed circuit, (b) Open circuit and (b) Short circuit.

47. What do you mean by closed circuit ?

Ans : Closed circuit is a complete electric circuit through which current will flow when voltage is applied.

48. What do you mean by open circuit ?

Ans : A break in a circuit not having a complete path or circuit for the flow of electric current is said to be open circuit or break circuit.

49. What do you mean by short circuit ?

Ans : An accidental connection of negligible resistance joining two wires of different polarity of a circuit, through which nearly all the current will flow, is said to be short circuit.

50. What are the combinations of resistances ?

Ans : There are three combinations of resistances : - Series combination (2) parallel combination and (3) series parallel mixed combination.

51. What is a series circuit ?

Ans : Series circuit is a circuit in which the same current flows through all the devices.

52. What are the characteristics of a series circuit ?

Ans : The followings are the characteristics of a series circuit : The same current passes through all the resistances in series circuit. Total voltage drop across the combination is the sum of the voltage drop across each resistance. The total or equivalent resistance which is the sum of the component resistance increases.

53. What is a parallel circuit ?

Ans : the Parallel circuit is a multiple circuits where the current divides and part flows through each device connected to it.

54. What are the characteristics of a parallel circuit ?

Ans : The following are the characteristics of a parallel circuit :- The total current divides and is the sum of the currents flowing through each resistance. Same voltage is applied across each resistance. The total or equivalent resistance is less than the least component i.e decreases.

55. What will be the total resistance when three equal resistances are connected in (a) Series and (b) parallel ?

Ans : (a) In series, total resistance, R_eq = R+R+R = 3R. i.e. three times of each resistance. (b) In parallel : 1/R_eq = 1/R + 1/R + 1/R = 3/R or R_eq = R/3 i.e. total resistance is equal to 1/3rd of each resistance.

56. What is conductance ?

Ans : It is the property of a material for easy conducting the current. Its unit is mho.

57. What are (a)E.M.F, (b) Potential Difference & (c) Current ?

Ans : (a) Electromotive force (E.M.F) is that force which creates the pressure to cause a flow of electrons through a conductor in any closed circuit. Potential difference between two points in a circuit is the electrical pressure or voltage required to drive the current between them. Current is the rate at which the electrons flow in any conductor.

58. What is voltage ?

Ans : Voltage is the potential, potential difference or electromotive force of a supply of electricity measured in volts.

59. What are the units of E.M.F, Potential Difference and current ?

Ans : The unit of E.M.F and the potential difference is volt. and the unit of current is ampere.

60. What is voltage drop ?

Ans : Voltage drop or potential drop is the diminution of potential along a conductor or in an apparatus through which a current is passing against its resistance.

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