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NCERT Solutions for class 12 Physics | Chapter 7 - Alternating Current

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Free download in PDF Class 12 Physics Chapter 7 Alternating Current Induction Multiple Choice Questions and Answers for Board, JEE, NEET, AIIMS, JIPMER, IIT-JEE, AIEE and other competitive exams. MCQ Questions for Class 12 Physics with Answers were prepared based on the latest exam pattern. These short solved questions or quizzes are provided by Gkseries. These will help the students for preparation of their examination./p>

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(1) A transformer works on the principle of
[A] self induction
[B] electrical inertia
[C] mutual induction
[D] magnetic effect of the electrical current
Answer: mutual induction
(2) Quality factor and power factor both have the dimensions of
[A] time
[B] frequency
[C] work
[D] angle
Answer: angle

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(3) At resonance frequency the impedance in series LCR circuit is
[A] maximum
[B] minimum
[C] zero
[D] infinity
Answer: minimum
(4) 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
[A] 30°
[B] 45°
[C] 60°
[D] 0°
Answer: Lenz’s law is a consequence of the law of conservation of momentum.
(5) At resonant frequency the current amplitude in series LCR circuit is
[A] maximum
[B] minimum
[C] zero
[D] infinity
Answer: maximum
(6) In which of the following circuits the maximum power dissipation is observed?
[A] Pure capacitive circuit
[B] Pure inductive circuit
[C] Pure resistive circuit
[D] None of these
Answer: Pure resistive circuit
(7) In a pure capacitive circuit if the frequency of ac source is doubled, then its capacitive reactance will be
[A] remains same
[B] doubled
[C] halved
[D] zero
Answer: halved
(8) Alternating voltage (V) is represented by the equation
[A] V(t) = Vm eωt
[B] V(t) = Vm sin ωt
[C] V(t) = Vm cot ωt
[D] V(t) = Vm tan ωt
Answer: V(t) = Vm sin ωt
(9) Which of the following graphs represents the correct variation of capacitive reactance Xc with frequency v u?
[A]
[B]
[C]
[D]
Answer:
(10) For an ideal-step-down transformer, the quantity which is constant for both the coils is
[A] current in the coils
[B] voltage across the coils
[C] resistance of coils
[D] power in the coils
Answer: power in the coils
(11) 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?
[A] Only resistor
[B] Resistor and inductor
[C] Resistor and capacitor
[D] Only inductor
Answer: Resistor and capacitor
(12) The rms value of potential difference V shown in the figure is

[A] V0/√3
[B] V0
[C] V0/√2
[D] V0/2
Answer: V0/√2
(13) Two coils X and Y are connected in series across a 240 V, 50 Hz supply. The resistance of X is 5Ω and inductance of Y is 0.02 H. The power consumed is 3 kW and the power factor is 0.75. The impedance of the circuit is:
[A] 0.144 Ω
[B] 1.44 Ω
[C] 14.4 Ω
[D] 144 Ω
Answer: 14.4 Ω
(14) In pure inductive circuit current
[A] lags behind emf by π/2
[B] leads the emf by π/2
[C] lags behind emf by π
[D] leads the emf by π
Answer: lags behind emf by π/2
(15) Faraday constant:
[A] depends on the amount of the electrolyte
[B] depends on the current in the electrolyte
[C] is a universal constant
[D] depends on the amount of charge passed through the electrolyte
Answer: is a universal constant
(16) A rejector circuit is:
[A] series resonant circuit
[B] parallel resonant circuit
[C] LCR circuit
[D] None of these
Answer: parallel resonant circuit
(17) The current through an inductor of 1H is given by I = 3t sin t. The voltage across the inductor of 1 H is:
[A] 3 sin t + 3 cos t
[B] 3 sin t + 3t cos t
[C] 3 cos t + t sin t
[D] 3t cos t + sin t
Answer: 3 sin t + 3t cos t
(18) The inductive reactance of an inductor coil of 1/π H at 50 Hz is:
[A] 50/π Ω
[B] π/50 Ω
[C] 100 Ω
[D] 50 Ω
Answer: 100 Ω
(19) In the series L-C-R circuit, the voltmeter and ammeter readings are:

[A] V = 100 Volts, I = 2A
[B] V = 100 Volts, I = 5A
[C] V = 1000 Volts, I = 2A
[D] V = 300 Volts, I = 1A
Answer: V = 100 Volts, I = 2A
(20) The phase difference b/w the A.C. and e.m.f. π/2 Which of the following can not be the instituent of the circuit?
[A] LC
[B] L alone
[C] C alone
[D] RL
Answer: RL

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