JEE Questions for Physics Alternating Current Quiz 7 - MCQExams.com

An alternating current is given by the equation i = i1cosωt + 2 sin ωt. The r.m.s. current is given by

  • Physics-Alternating Current-61827.png
  • 2)
    Physics-Alternating Current-61828.png

  • Physics-Alternating Current-61829.png

  • Physics-Alternating Current-61830.png
In an ac circuit with voltage V and current I, the power dissipated is
  • VI
  • 2)
    Physics-Alternating Current-61832.png

  • Physics-Alternating Current-61833.png
  • Depends on the phase between V and I
A resistance of 20 ohms is connected to a source of an alternating potential V = 220 sin (100 πt). The time taken by the current to change from its peak value to r.m.s. value is
  • 0.2 sec
  • 0.25 sec

  • Physics-Alternating Current-61835.png

  • Physics-Alternating Current-61836.png

Physics-Alternating Current-61838.png
  • Voltage leads the current by 30°
  • Current leads the voltage by 30°
  • Current leads the voltage by 60°
  • Voltage leads the current by 60°
An ac source is rated at 220 V, 50 Hz. The time taken for voltage to change from its peak value to zero is
  • 50 sec
  • 0.02 sec
  • 5 sec

  • Physics-Alternating Current-61840.png
The phase angle between e.m.f. and current in LCR series ac circuit is

  • Physics-Alternating Current-61842.png
  • 2)
    Physics-Alternating Current-61843.png

  • Physics-Alternating Current-61844.png

  • Physics-Alternating Current-61845.png
Power delivered by the source of the circuit becomes maximum, when

  • Physics-Alternating Current-61846.png
  • 2)
    Physics-Alternating Current-61847.png

  • Physics-Alternating Current-61848.png

  • Physics-Alternating Current-61849.png

Physics-Alternating Current-61850.png

  • Physics-Alternating Current-61851.png
  • 10 A

  • Physics-Alternating Current-61852.png

  • Physics-Alternating Current-61853.png
  • 5A
Same current is flowing in two alternating circuits. The first circuit contains only inductance and the other contains only a capacitor. If the frequency of the e.m.f. of ac is increased, the effect on the value of the current will be
  • Increases in the first circuit and decreases in the other
  • Increases in both the circuits
  • Decreases in both the circuits
  • Decreases in the first circuit and increases in the other
The value of alternating e.m.f. E in the given circuit will be
Physics-Alternating Current-61856.png
  • 100 V
  • 20 V
  • 220 V
  • 140 V
The natural frequency of a L-C circuit is equal to

  • Physics-Alternating Current-61858.png
  • 2)
    Physics-Alternating Current-61859.png

  • Physics-Alternating Current-61860.png

  • Physics-Alternating Current-61861.png
In a series LCR circuit R = 200Ω and the voltage and the frequency of the main supply is 220 V and 50 Hz respectively. On taking out the capacitance from the circuit the current lags behind the voltage by 30°. On taking out the inductor from the circuit the current leads the voltage by 30°. The power dissipated in the LCR circuit is
  • 242 W
  • 305 W
  • 210 W
  • Zero W
An LCR series with R = 100Ω is connected to a 200 V, 50 Hz ac source when only the capacitance is removed, the current leads the voltage by 60°. When only the inductance is removed, the current leads the voltage by 60°. The current in the circuit is
  • 2A
  • 1A

  • Physics-Alternating Current-61863.png

  • Physics-Alternating Current-61864.png

Physics-Alternating Current-61866.png

  • Physics-Alternating Current-61867.png
  • 2)
    Physics-Alternating Current-61868.png

  • Physics-Alternating Current-61869.png
  • 1000 Hz
In an ac series circuit, the instantaneous current is maximum when the instantaneous voltage is maximum. The circuit element connected to the source will be
  • Pure inductor
  • Pure capacitor
  • Pure resistor
  • Combination of capacitor and inductor
For series LCR circuit, wrong statement is
  • Applied e.m.f. and potential difference across resistance are in same phase
  • Applied e.m.f. and potential difference at inductor coil have phase difference of π/2
  • Potential difference at capacitor and inductor have phase difference of π/2
  • Potential difference across resistance and capacitor have phase difference of π/2
In a purely resistive ac circuit, the current
  • Lags behind the e.m.f. in phase
  • Is in phase with the e.m.f.
  • Leads the e.m.f. in phase
  • Leads the e.m.f. in half the cycle and lags behind it in the other half
Two identical incandescent light bulbs are connected as show in figure. When the circuit is an ac voltage source of frequency f, which of the following observations will be correct
  • Both bulbs will glow alternatively
  • 2)
    Physics-Alternating Current-61871.png
  • Bulb b1 will light up initially and goes off, bulb b2 will be ON constantly
  • Bulb b1will blink and bulb b2will be ON constantly
An LCR circuit contains R = 50 Ω, L =1 mH and C = 0.1μF. The impedance of the circuit will be minimum for a frequency of

  • Physics-Alternating Current-61872.png
  • 2)
    Physics-Alternating Current-61873.png

  • Physics-Alternating Current-61874.png

  • Physics-Alternating Current-61875.png
A capacitor and an inductance coil are connected in separate ac circuits with a bulb glowing in both the circuits. The bulb glows more brightly when
  • An iron rod is introduced into the inductance coil
  • The number of turns in the inductance coil is increased
  • Separation between the plates of the capacitor is increased
  • A dielectric is introduced into the gap between the plates of the capacitor

Physics-Alternating Current-61877.png

  • Physics-Alternating Current-61878.png
  • 2)
    Physics-Alternating Current-61879.png
  • 100 ohm
  • 50 ohm
An inductor of inductance L and resistor of resistance R are joined in series and connected by a source of frequency ω. Power dissipated in the circuit is

  • Physics-Alternating Current-61881.png
  • 2)
    Physics-Alternating Current-61882.png

  • Physics-Alternating Current-61883.png

  • Physics-Alternating Current-61884.png
For the series LCR circuit shown in the figure, what is the resonance frequency and the amplitude of the current at the resonating frequency
Physics-Alternating Current-61886.png

  • Physics-Alternating Current-61887.png
  • 2)
    Physics-Alternating Current-61888.png

  • Physics-Alternating Current-61889.png

  • Physics-Alternating Current-61890.png
In the alternating current shown in the figure, the currents through inductor and capacitor are 1.2 amp and 1.0 amp respectively. The current drawn from the generator is
Physics-Alternating Current-61892.png
  • 0.4 amp
  • 0.2 amp
  • 1.0 amp
  • 1.2 amp
Q-factor can be increased by having a coil of
  • Large inductance, small ohmic resistance
  • Large inductance, large ohmic resistance
  • Small inductance, large ohmic resistance
  • Small inductance, small ohmic resistance
Current in the LCR circuit becomes extremely large when
  • Frequency of ac supply is increased
  • Frequency of ac supply is decreased
  • Inductive reactance becomes equal to capacitive reactance
  • Inductance becomes equal to capacitance
In a series LCR circuit the frequency of a 10 V, ac voltage source is adjusted in such a fashion that the reactance of the inductor measure 15Ω and that of the capacitor 11Ω. If R = 3Ω, the potential diffenrence across the series combination of L and C will be
  • 8 V
  • 10 V
  • 22 V
  • 52 V
A LCR series ac circuit is turned to resonace. The impedence of the circuit is now
  • R
  • 2)
    Physics-Alternating Current-61895.png

  • Physics-Alternating Current-61896.png

  • Physics-Alternating Current-61897.png
An LCR series ac circuit is at resonance with 10 V each across L, C and R. If the resistance is halved, the respective voltages across L, C and R are
  • 10 V, 10 V and 5 V
  • 10 V, 10 V and 10 V
  • 20 V, 20 V and 5 V
  • 20 V, 20 V and 10 V
  • 5 V, 5 V and 5 V
An LCR series circuit is at resonance. Then
  • The phase difference between current and voltage is 90°
  • The phase difference between current and voltage is 45°
  • Its impedance is purely resistive
  • Its impedance is zero
  • The current is minimum
A fully charged capacitor C with initial charge q0, is connected to a coil of self inductanceL at t = 0. The time at which the energy is stored equally between theelectric and the magnetic fields is

  • Physics-Alternating Current-61900.png
  • 2)
    Physics-Alternating Current-61901.png

  • Physics-Alternating Current-61902.png

  • Physics-Alternating Current-61903.png
An ac voltage source of variable angular frequency ω and fixed amplitude V connected in series with a capacitance C and an electric bulb of resistance R (inductance zero). When ω is increased
  • The bulb glows dimmer
  • The bulb glows brighter
  • Total impedence of the circuit is unchanged
  • Total impedence of the circuit increases
In the circuit shown in figure neglecting source resistance the voltmeter and ammeter reading will respectively be
Physics-Alternating Current-61906.png
  • 0 V, 3A
  • 150 V, 3A
  • 150 V, 6A
  • 0 V, 8 A

Physics-Alternating Current-62053.png

  • Physics-Alternating Current-62054.png
  • 2)
    Physics-Alternating Current-62055.png

  • Physics-Alternating Current-62056.png

  • Physics-Alternating Current-62057.png
In the circuit shown in the figure, the ac source gives a voltage V = 20 cos (2000 t). Neglecting source resistance, the voltmeter and ammeter reading will be
Physics-Alternating Current-61908.png
  • 0 V, 0.47A
  • 1.68 V, 0.47A
  • 0 V, 1.4 A
  • 5.64 V, 1.4 A
The reading of ammeter in the circuit shown will be
Physics-Alternating Current-61910.png
  • 2A
  • 2.4 A
  • zero
  • 1.7 A
Is it possible
Physics-Alternating Current-61912.png
  • Yes
  • No
  • Cannot be predicted
  • Insufficient data to reply
Which of the following curves represents the variation of impedance (Z) with frequency f in series LCR circuit

  • Physics-Alternating Current-61914.png
  • 2)
    Physics-Alternating Current-61915.png

  • Physics-Alternating Current-61916.png

  • Physics-Alternating Current-61917.png
The variation of the instantaneous current (I) and the instantaneous e.m.f. (E) in a circuit is as shows in fig.
Which of the following statement is correct
Physics-Alternating Current-61919.png
  • The voltage lags behind the current by π/2
  • The voltage leads the current by π /2
  • The voltage and the current are in phase
  • The voltage leads the current by π
An alternating e.m.f is applied across a parallel combination of a resistance R, capacitance C and an inductance L. If IR, IL, IC are the currents through R, L and C respectively, then the diagram which correctly represents the phase relationship among IR, IL, IC and source e.m.f. E, is given by

  • Physics-Alternating Current-61921.png
  • 2)
    Physics-Alternating Current-61922.png

  • Physics-Alternating Current-61923.png

  • Physics-Alternating Current-61924.png
An ac source of variable frequency f is connected to an LCR series circuit. Which of the graphs in figure represents the variation of current I in the circuit with frequency f

  • Physics-Alternating Current-61926.png
  • 2)
    Physics-Alternating Current-61927.png

  • Physics-Alternating Current-61928.png

  • Physics-Alternating Current-61929.png
The r.m.s. voltage of the wave form shown is
Physics-Alternating Current-61931.png
  • 10 V
  • 7 V
  • 6.37 V
  • None of these
The output current versus time curve of a rectifier is shown in the figure. The average value of output current in this case is
Physics-Alternating Current-61933.png
  • 0
  • 2)
    Physics-Alternating Current-61934.png

  • Physics-Alternating Current-61935.png

  • Physics-Alternating Current-61936.png
Two sinusoidal voltage of the same frequency are shown in the diagram. What is the frequency, and the phase relationship between the voltages
Physics-Alternating Current-61938.png
  • a
  • b
  • c
  • d
In pure inductive circuit, the curve between frequency f and reciprocal of inductive reactance 1/XL is

  • Physics-Alternating Current-61940.png
  • 2)
    Physics-Alternating Current-61941.png

  • Physics-Alternating Current-61942.png

  • Physics-Alternating Current-61943.png
The resonance point in XL – f and XC – f is
Physics-Alternating Current-61945.png
  • P
  • Q
  • R
  • S
The i – v curve for anti-resonance circuit is

  • Physics-Alternating Current-61947.png
  • 2)
    Physics-Alternating Current-61948.png

  • Physics-Alternating Current-61949.png

  • Physics-Alternating Current-61950.png
Which of the following curves correctly represents the variation of capacitive reactance XC with frequency f ?

  • Physics-Alternating Current-61951.png
  • 2)
    Physics-Alternating Current-61952.png

  • Physics-Alternating Current-61953.png

  • Physics-Alternating Current-61954.png
Assertion The alternating currents lags behind the e.m.f. by a phase angle of π/2, when ac flows through an inductor.
Reason The inductive reactance increases as the frequency of ac source decreases.
  • If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion
  • If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion
  • If Assertion is true but Reason is false.
  • If the Assertion and Reason both are false.
  • If Assertion is false but Reason is true.
Assertion In series LCR circuit resonance can take place.
Reason Resonance takes place if inductance and capacitive reactances are equal and opposite.
  • If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
  • If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
  • If Assertion is true but Reason is false.
  • If the Assertion and Reason both are false.
  • If Assertion is false but Reason is true.
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