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Physics Quiz 1 Chapter 7
Alternating Current
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Q .1 An electrical element X when connected to an alternating voltage source has current through it leading the voltage by π/2 radian. Identify X
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(a) Capacitor
(b) Resistor
(c) Inductor
(d) Series LR ckt.
Q. 2
Average power dissipated in an ideal inductor in a.c. circuit is:
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(a) Infinte
(b) 100
(c) Zero
(d) one
Q. 3 A Capacitor blocks
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(a) Only a.c
(b) Only d.c.
(c) Both ac and dc
(d) None of these.
Q.4 A transformer steps up 220 V to2200 V. What is the transformation ratio?
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(a) 20
(b) 0.1
(c) 0.2
(d) 10
Q.5 In which of the following circuits the maximum power dissipation is observed?
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(a) Pure capacitive circuit
(b) Pure inductive circuit
(c) Pure resistive circuiton
(d) None of these
Q.6 The instantaneous current in an ac circuit is i=2.0 sin314t, what is its frequency?
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(a) 100 Hz
(b) 60 Hz
(c) 50 Hz
(d) 2π
Q.7 The instantaneous current in an ac circuit is i=2.0 sin314t, what is rms value of the current
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(a) 1.414 A
(b) 2√2A
(c) 1 A
(d) 2 A
Q.8 An L,C, R series circuit is connected to a.c. source. At resonance, the applied voltage and the current flowing through the circuit will have a phase difference of
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(a) π/4
(b) zero
(c) π
(d) π/2
Q.9 In an a.c. circuit, containing an inductance and a capacitor in series, the current is found to be maximum when the value of inductance is 0.5henry and of capacitance is 8μF. The angular frequency of the input A.C. Voltage must be equal to
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(a) 500
(b) 1000
(c) 4000
(d) 2000
Q.10
In a transformer, number of turns in the primary are 140 and that in the secondary are 280. If current in primary is 4A, then that in the secondary is
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(a) 4 A
(b) 2 A
(c) 6 A
(d) 10 A
Q.11 In a series LCR circuit, resistance R = 10 and the impedance Z = 20. The phase difference between the current and the voltage is
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(a) 30
(b) 45
(c) 60
(d) 90
Q.12 In the case of an inductor :
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(a) voltage lags the current by π/2
(b) voltage leads the current by π/2
(c) voltage leads the current by π
(d) voltage leads the current by π/3
Q.13
In an AC circuit, V and I are given by V=150 sin (150t) volts and I = 150 sin (150t) amperes. The power dissipated in the circuit is:
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(a) 11250 Watt
(b) 12250 Watt
(c) 1125 Watt
(d) 250 Watt
Q. 14 An A.C source is connected to a resistive circuit. Which of the following is true ?
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(a) Current leads the voltage and both are in same phase
(b) Current lags behind the voltage and both are in same phase
(c) Current and voltage are in same phase
(d) Any of the above may be true depending upon the value of resistance
Q.15 The output voltage of an ideal transformer, connected to a 240V a.c. mains is 24V. When this transformer is used to light a bulb with rating (24V, 24W), calculate the current in the primary coil of the circuit.
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(a) 0.3A
(b) 0.1A
(c) 0.8A
(d) 1.02A
Q. 16 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
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(a) 50 V
(b) 50√2 V
(c) 100 V
(d) zero
Q. 17 The core of any transformer is laminated so as to.
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(a) reduce the energy loss due to eddy currents
(b) make it light weight
(c) make it robust and strong.
(d) increase the secondary voltage.
Q. 18 For an ideal-step-down transformer, the quantity which is constant for both the coils is.
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(a) current in the coils
(b) voltage across the coils
(c) resistance of coils
(d) power in the coils
Q.19 To reduce the resonant frequency in an LCR series circuit with a generator .
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(a) the generator frequency should be reduced
(b) another capacitor should be added in parallel to the first.
(c) the iron core of the inductor should be removed.
(d) dielectric in the capacitor should be removed.
Q. 20 When an AC voltage of 220 V is applied to the capacitor C .
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(a) the maximum voltage between plates is 220 V
(b) the current is in phase with the applied voltage.
(c) the charge on the plates is not in phase with the applied voltage.
(d) power delivered to the capacitor is zero.
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