# Basic Electrical interview Questions & Answers paper-4

61. Is it possible to measure E.M.F ? If not, why ?

Ans : The E.M.F can not be measured but can be calculated in the way :-
E.M.F = Terminal voltage + Voltage drop inside the source of supply.
The E.M.F can not be measured because the measuring instrument will cause some voltage drop due to consumption of some energy and the actual value will not come in appearance.

62. What is potential gradient ?

Ans : The potential gradient is the space rate of change of potential with respect to distance.

63. When a larger number of lamps are connected in (a)Series and (b) Parallel what will happen to other lamps if one lamp is fused ?

Ans : (a) None will glow due to break circuit . Other lamps will glow as usual.

64. What do you understand by E.M.F and potential difference of a call ?

Ans : The voltage across the terminals of a cell in open circuit is called E.M.F of a cell, and the voltage across the terminals of a cell on load is called the potential difference of a cell.

65. How will you connect the cell (a)to increase the e.m.f and (b) to increase the supply of current ?

Ans : (a) In series and (b) In parallel.

66. What will be the e.m.f of a battery of 6 cells each 2 volts if the cells are connected in (a) Series and (b) Parallel ?

Ans : (a) 6 × 2V = 12 volts and (b) 2 volts.

67. What will be the internal resistance of a battery of 6 cells each of 0.3 ohm if the cells are connected in (a) Series and (b) Parallel ?

Ans : (a) 0.3 ohm × 6 = 1.8 ohms (b) 0.3 ohm ÷ 6 = 0.05 ohm.

68. Define kirchhoff’s laws ? Are they applicable to both a.c. and d.c. circuits ?

Ans : (a) Current Law :- In any network of wires the algebraic sum of the electric currents which meet at a point is zero.
Voltage law :- The algebraic sum of the electromotive forces in any closed circuit or mesh is equal to the algebraic sum of the products of the resistance of each portion of the circuit and the currents flowing through them.
Kirchhoff’s laws are applicable to both a.c and d.c circuit. In case of a.c circuit any e.m.f of self inductance or that existing across a capacitor should be taken into account.

69. What do you mean by electrical network ?

Ans : An electrical network is a collection of electric elements such as resistors, coils, capacitors and sources of energy connected together to form several interrelated circuits for the purpose of satisfying specified requirements.

70. What do you mean by active and passive network ?

Ans : Active network means the electric network which contains one or more sources of e.m.f’s in if passive network means the electric network in which there is no source of e.m.fs.

71. What do you mean by linear and non linear network ?

Ans : Linear network also known as linear circuit means the network of electrical elements in which the parameters of resistance, inductance and capacitance are constant with respect to current or voltage and in which the voltage or current of sources is independent of or directly proportional to other voltages and currents or their derivatives in the net work. Non liner network also known as non linear circuit means the network of electrical elements in which the parameters are not constant but change with respect to current or voltage.

72. What do you mean by bilateral and unilateral circuit ?

Ans : Bilateral circuit means the electrical circuit which has same properties or characteristics in both directions, e.g. transmission line. Unilateral circuit means the electrical circuit in which the properties or characteristics change with the change in direction e.g. vacuum tube rectifier.

73.What do you mean by “Eddy Current” ?

Ans : Eddy current or Foucault current means the current induced in the interior of conducting masses by variation of the magnetic flux.

74. What do you mean by “Skin Effect” ?

Ans : Skin effect means the action of alternating current that causes more of a current to flow near the outside surface that in the centre of a conductor.

75. Define Electrical Work, Electrical power & Electrical Energy ?

Ans : Electrical work is said to be done when an electric charge flows under a potential difference.
In mechanic power is simply the rate of doing work. Electrical power is the rate of transfer of electrical energy i.e the rate of electrical work done to mark a flow of change ‘Q’ under a potential difference ‘V’.
In mechanics energy is simply the capacity of doing work. Electrical energy is the amount of work done which is equal to the product of the rate of doing work by time i.e power x time.

76. What are the units of electrical power and electrical energy ?

Ans : The unit of electrical power is watt. The bigger units are kilo watt (1000 watt) and Mega watt = (〖10〗^6watt). The unit of electrical energy is watt hour (Wh). The bigger unit s kilo watt hour (kwh = 1000 Wh).

77.Define “British H.P” and “Metric H.P”.

Ans : British horse power is said to be the mechanical unit of power in F.P.S. system when it does the work at the rate of 550 ft lbs/sec or 33,000 ft lbs/min,
Metric horse power is said to be the mechanical unit of power in M.K.S. system when it does the work at the rate of 75 kg-m/sec or 4500 kg-m/minute.

78. What is the relation between H.P. and kW. ?

Ans : 1 H.P (Bitish) = 746 watts = 0.746 kW.
H.P (Metric) = 735.5 watts = o.7355 kW.

79. Give three formulas for power.

Ans : W = V2/R ,
W = V.I,
W = I2R.

80.What is the relation among power, resistance and volts ?

Ans : Power (W) = ([Voltage (V)]2)/(Resistance (R))
In unit relation, Watt = ((Volts)2)/(Ohm.)

81. What is B.O.T.U. ?

Ans : Board of Trade unit (B.O.T.U) is the commercial unit of electrical energy on the basic of which electrical energy is charged. It is also known as k.W.h. unit.

82.How will you calculate the resistance of a lamp from the monogram of given voltage and watt ?

Ans : From the formula of power, W =V2/R Resistance = ((Voltage)2)/Wattage i.e R =V2/W

83. Whose resistance is more between one 25 watt and one 200 watt lamp of same voltage.

Ans : R = V2/W. Resistance is inversely proportional to wattage of lamp, voltage remaining same.
Therefore, the resistance of lower wattage 25 W lamp will be more than higher wattage 200 W. lamp.

84. What will happen when one 110 volt, 25 watt lamp and one 11ovolt, 200 watt lamp are connected in series with 220 volts supply ?

Ans : Voltage drop being higher than its rated voltage across higher resistance of W lamp it will burst.

85. How much energy will be consumed by a 220 volt, 60 watt lamp when it is connected in 110 volts supply ?

Ans : From the formula W = V2/R, resistance of the lamp remaining same power consumed is proportional to square of the voltage. Therefore when voltage is reduced to half the rated voltage the power consumption will be reduced to (1/2)2 or ¼ of 60W i.e 15 watt.

86. A 1000 watt heater has a wire length of 5 meters. What will be the capacity of the heater if the length of the wire is halved ?

Ans : The power W1 = V2/R
The resistance will be halved for half length.
Therefore W2 = V2/(R/2) = 2. V2/R = 2× W1
If W1 =1000 W. then for half length, W2 = 2 × 1000W = 2000W.