# Objective Type Question or MCQ of Electrical Circuits and Magnetic Fields page-6

76. An arc across the switch opening an R-L circuit is a result is a result of the

a) Long time constant
b) Large self-induced voltage across the inductance
c) Source of the voltage caused by IR drop across the resistance
d) Low resistance of the open switch

Ans: (b)

77. In a sine wave a.c. circuit with a resistive branch and inductive branch in parallel, the

a) Voltage across the inductor leads the voltage across the reactance by 90°
b) Resistance branch current is 90° out of phase with the inductive branch current
c) Resistive and inductive branch current are 180° out of phase
d) Inductive and resistive branch currents are in phase

Ans: (b)

78. A.d.c. voltage of 12 volts applied across an inductance in series with a switch

a) Can produce the induced voltage as the current decreases when the switch is opened
b) Cannot produce the induced voltage as the voltage applied has the one polarity
c) Produces more induced voltage when the switch is closed than the switch is opened
d) None of the above

Ans: (a)

79. Alternating current in the inductance will produce maximum induced voltage when the current has its

a) Maximum value
b) Maximum change in magnetic field
c) Minimum change in magnetic field
d) 0.707 × Peak

Ans: (b)

80. Two 300-mh chokes connected in series will have the total inductance of

a) 60 mh
b) 300 mh
c) 150 mh
d) 600 mh

Ans: (d)

81. Which of the following statements is true?

a) Iron core has maximum eddy-current losses
b) Laminated iron core has minimum eddy-current losses
c) Power-iron core has the maximum eddy-current losses
d) Air core has the minimum eddy-current

Ans: (d)

82. Two waves have the frequency of 500 Hz and one is set at its maximum value whereas the other at zero, the phase angle between them will be

a) 0°
b) 180°
c) 360°
d) 90°

Ans: (d)

83. Which of the following statements is true?

a) Ceramic capacitors must be connected in the correct polarity
b) Electrolytic capacitor must be connected in the correct polarity
c) Mica capacitors are available in capacitance value of 1 to 10 micro-farad
d) Air capacitors have a blackband to indicate the outside foil

Ans: (b)

84. Voltage applied across a ceramic dielectric produces an electrolytic field 100 times greater than air. What will be the value of dielectric constant?

a) 33.333
b) 50
c) 1000
d) 100

Ans: (d)

85. If an a.c. voltage is applied to capacitive circuit, the alternating current can flow in the circuit because

a) Of high peak value
b) Charging current can flow
c) Discharge current can flow
d) Varying voltage produces the charging and discharging currents

Ans: (d)

86. The amount of capacitive reactance with higher frequencies

a) Decreases
b) Increases
c) Remains same for frequencies
d) Decreases as the voltage increases

Ans: (a)

87. A steady d.c. voltage is applied to capacitor, after changes to battery voltage, the current in the circuit

a) Depends on the current rating of the battery
b) Is greater for larger values of capacitances
c) Is smaller for larger values of capacitances
d) Is zero for any value of capacitance

Ans: (d)

88. In sine wave a.c. circuit with Xc and R in series, the

a) Voltages across R and Xc are in phase
b) Voltages across R and Xc are 180° out of phase
c) Voltages across R leads the voltages across Xc by 90°
d) Voltage across R lags the voltage across Xc by 90°

Ans: (c)

89. A capacitor can store the change because it has dielectric between two conductors.

a) True
b) False

Ans: (a)

90. The thinner the dielectric the more the capacitance and lower is the voltage breakdown rating for a capacitor

a) True
b) False

Ans: (a)

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