Objective Type Questions for SSC JE Electrical

81. Magnetic blowout coils are generally used in

(a) oil circuit breaker
(b) vaccum circuit breaker
(c) air break circuit breaker
(d) air blast circuit breaker

82. The pitch factor for a full pitched winding of a synchronous machine is

(a) 1.0
(b) 0.5
(c) 0.9
(d) 0.0

83. An AC meter of resistance Rm and resistance Xm is connected in series with a resistance Rs. A shunt of impedance (Rsh + jXsh) is applied in parallel to the existing combination of meter and Rs. The current division across the two branches will be independent of frequency when

84. In phantom loading arrangement, energy consumption in the calibration test of wattmeter is reduced because of

(a) the absence of load in the test set
(b) the separate application of low voltage supply across current coil
(c) no common point between the two coils
(d) the reduced loss in current coil and pressure coil

85. In the measurement of power in a balanced 3-phase circuit by two-wattmeter method if the two wattmeters show equal readings, then the power factor of the circuit is

(a) 0.8 leading
(b) zero
(c) unity
(d) 0.8 lagging

86. Two meters X and Y required 40mA and 50mA respectively for fully scale deflection. Then

(a) Y is more sensitive than X
(b) Both are equally sensitive
(c) Data are insufficient to comment
(d) X is more sensitive than Y

Answer: (d) X is more sensitive than Y

87. The household energy meter is

(a) integrating instrument
(b) recording instrument
(c) None of these
(d) indicating instrument

88. A Ballistic galvanometer of constant equal to 1 micro-coulomb/degree gives a throw of 22.5^o, when a capacitor discharges through the meter. If a battery of 15V is used to recharge the capacitor, value of capacitance is

(a) 15 μF
(b) 22.5 μF
(c) 10 μF
(d) 1.5 μF

Answer: (d) 1.5 μF

89. A potentiometer is used to measure the voltage between two points of a DC circuit, which is found to be 1.2V. This is also measured by a voltmeter, which is found to be 0.9V. The resistance of the voltmeter is 60 kΩ The input resistance between two points

(a) 80 k Ω  
(b) 60 k Ω
(c) 20 k Ω  
(d) 45 k Ω

Answer: (c) 20 k Ω  

90. A load is connected to supply. A current transformer (CT), and a potential transformer (PT) is used in between load and supply. A power factor of 0.5 is measured at the secondary side of CT and PT . If phase angle error of CT and PT are 0.4^o and 0.7^o, power factor of the load is

(a) cos 61.1°
(b) cos 60.3°
(c) cos 58.9°
(d) cos 59.7°

91. During the measurement of a low resistance using a potentiometer, the following readings were obtained: Voltage drop across unknown resistance = 0.531V. Voltage drop across a 0.1 Ω   standard resistance connected in series with the unknown = 1.083V. Value of the unknown resistor is

(a) 53.1 milliohm
(b) 49.03 milliohm
(c) 108.3 milliohm
(d) 20.4 milliohm

92. Which one of the following types of instruments does suffer from error due to magnetic tysteresis?

(a) PMMC
(b) Induction type
(c) Electrodynamic
(d) Moving iron

93. Which one of the following does not employ a null method of measurement?

(a) AC potentiometer
(b) Megger
(c) DC potentiometer
(d) Kelvin double bridge

94. In star-delta starting of three-phase induction motor the starting voltage is reduced to

(a) 1/√3 times of normal voltage
(b) √3 times of normal voltage
(c) 3 times of normal voltage
(d) 1/3 times of normal voltage

95. An electromagnetic torque is produced as an interaction between a flux and current. The angle between flux and current is 45°. If this angle is change to 30, flux increases by 100% and current reduces by 25%, then the torque

(a) reduces to 66.7% of the original
(b) increases to 81.6% of teh original
(c) reduces to 81.6.7% of the original
(d) reduces to 54.4% of the original

Answer: (b) increases to 81.6% of the original

96. Minimum temperature limit for class F insulation is

(a) 155 °C
(b) 130 °C
(c) 120 °C
(d) 105 °C

98. The motor characteristics best suited for traction purpose are those of

(a) DC shunt motor
(b) DC series motror
(c) synchronous motor
(d) induction torque

99. If the starting torque of a 3-phase induction motor is Tst for DOL starting, that star-delta starting of the motor is

(a) 3 T_st
(b) T_st/3
(c) T_st / √3
(d) √3T_st

100. The iron loss in a 100 KVA transformer is 1kW and at full load copper loss is 2 kW. The maximum efficiency occurs at a load of

(a) 50 KVA
(b) 100 KVA
(c) 70.7 KVA
(d) 14.4 KVA