Q. The phase difference between the alternating current and emf is TE/2. Which ofthe following cannot be the constituent of the circuit?
β
Correct Answer: (C)
L and C
Alternating Current MCQs with answers
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Q. In an LCR-series ac circuit, the voltage across each of the component L, C and R is 50 V. The voltage across the LC-combination will be
β
Correct Answer: (D)
zero
Q. An ac circuit has a resistance of 12 ohm and an impedance of 15 ohm. The power factor of the circuit will be
β
Correct Answer: (A)
0.8
Q. In an LCR circuit, capacitance is charged from C to 2C. For resonant frequency to remain unchanged, the inductance should be changed from L to
β
Correct Answer: (C)
L/2
Q. The core of any transformer is laminated so as to
β
Correct Answer: (A)
reduce the energy loss due to eddy currents.
Q. In an a.c. generator, a coil with N turns, all of the same area A and total resistance R, rotates with frequency Ο in a magnetic field B the maximum value of emf generated in the coil is
β
Correct Answer: (B)
NABΟ
Q. Which quantity is increased in a step-down transformer?
β
Correct Answer: (A)
Current
Q. If an AC voltage is applied to an ICi? circuit, which of the following is true?
β
Correct Answer: (C)
I and V are out of phase in both C and L.
Q. A transformer is used to light a 100 W and 110 V lamp from a 220 V mains. If the main current is 0.5 A, the efficiency of the transformer is approximately
β
Correct Answer: (C)
90%
Q. Choose the correct statement.
β
Correct Answer: (B)
In a dc circuit the inductor can conduct but not a capacitor.
Q. A coil of self-inductance L is connected in series with a bulb B and an ac source. Brightness of the bulb decreases when
β
Correct Answer: (D)
an iron rod is inserted in the coil.
Q. The reactance of a capacitor C is X. If both the frequency and capacitance be doubled, then new reactance will be
β
Correct Answer: (D)
X/4
Q. The line that draws power supply to your house from street has
β
Correct Answer: (A)
zero average current
Q. In an alternating current circuit consisting of elements in series, the current increases on increasing the frequency of supply. Which of the following elements are likely to constitute the circuit?
β
Correct Answer: (C)
Resistor and capacitor
Q. In which of the following circuits the maximum power dissipation is observed?
β
Correct Answer: (C)
Pure resistive circuit
Q. In a series LCR circuit the voltage across an inductor, capacitor and resistor are 20 V, 20 V and 40 V respectively. The phase difference between the applied voltage and the current in the circuit is
β
Correct Answer: (D)
0Β°
Q. At resonance frequency the impedance in series LCR circuit is
β
Correct Answer: (B)
minimum
Q. At resonant frequency the current amplitude in series LCR circuit is
β
Correct Answer: (A)
maximum
Q. Quality factor and power factor both have the dimensions of
β
Correct Answer: (D)
angle
Q. Alternating current cannot be measured by dc ammeter, because
β
Correct Answer: (A)
ac cannot pass through ac ammeter.
Q. In a pure capacitive circuit if the frequency of ac source is doubled, then its capacitive reactance will be
β
Correct Answer: (C)
halved
Q. For an ideal-step-down transformer, the quantity which is constant for both the coils is
β
Correct Answer: (D)
power in the coils
Q. To reduce the resonant frequency in an LCR series circuit with a generator
β
Correct Answer: (B)
another capacitor should be added in parallel to the first.
Q. Which of the following combinations should be selected for better tuning of an LCR circuit used for communication?
β
Correct Answer: (C)
R = 15 , L = 3.5 H, C = 30 ΞΌF
Q. An inductor of reactance 1 β¦ and a resistor of 2 β¦ are connected in series to the terminals of a 6 V (rms) a.c. source. The power dissipated in the circuit is
β
Correct Answer: (C)
14.4 W.
Q. The output of a step-down transformer is measured to be 24 V when connected to a 12 watt light bulb. The value of the peak current is
β
Correct Answer: (A)
1/β2 A.
Q. As the frequency of an ac circuit increases, the current first increases and then decreases. What combination of circuit elements is most likely to comprise the circuit?
β
Correct Answer: (A)
Inductor and capacitor.
Q. When an AC voltage of 220 V is applied to the capacitor C
β
Correct Answer: (D)
power delivered to the capacitor is zero.
Q. Electrical energy is transmitted over large distances at high alternating voltages. Which of the following statements is not correct?
β
Correct Answer: (C)
Transmission lines can be made thinner.
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