JEE Questions for Physics Alternating Current Quiz 8 - MCQExams.com

Assertion Capacitor serves as a block for dc and offers an easy path to ac. .
Reason Capacitive reactance is inversely proportional to frequency.
  • 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 When capacitive reactance is smaller than the inductive reactance in LCR circuit, e.m.f. leads the current.
Reason The phase angle is the angle between the alternating e.m.f. and alternating current of the circuit.
  • 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 A capacitor of suitable capacitance can be used in an ac circuit in place of the choke coil.
Reason A capacitor blocks dc and allows ac only.
  • 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 If the frequency of alternating current in an ac circuit consisting of an inductance coil is increased then current gets decreased.
Reason The current is inversely proportional to frequency of alternating current.
  • 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 An inductance and a resistance are connected in series with an ac circuit. In this circuit the current and the potential difference across the resistance lags behind potential difference across the inductance by an angle π/2.
Reason In LR circuit voltage leads the current by phase angle which depends on the value of inductance and resistance both.
  • 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 An alternating current does not show any magnetic effect.
Reason Alternating current varies with time.
  • 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 The dc and ac both can be measured by a hot wire instrument.
Reason The hot wire instrument is based on the principle of magnetic effect of current.
  • 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 ac is more dangerous than dc.
Reason Frequency of ac is dangerous for human body.
  • 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 Average value of ac over a complete cycle is always zero.
Reason Average value of ac is always defined over half cycle.
  • 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 The divisions are equally marked on the scale of ac ammeter.
Reason Heat produced is directly proportional to the current.
  • 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.
The instantaneous value of current in an ac circuit is I = 2 sin (100 πt + π/A. The current will bemaximum for the first time at

  • Physics-Alternating Current-62059.png
  • 2)
    Physics-Alternating Current-62060.png

  • Physics-Alternating Current-62061.png

  • Physics-Alternating Current-62062.png
Assertion For an electric lamp connected in series with a variable capacitor and ac source, its brightness increases with increase in capacitance.
Reason Capacitive reactance decreases with increase in capacitance of capacitor.
  • 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.
The self inductance of a choke coil is 10 mH. When it is connected with a 10 V dc source, then the loss of power is 20 watt. When it is connected with 10 volt ac source loss of power is 10 watt. The frequency of ac source will be
  • 50 Hz
  • 60 Hz
  • 80 Hz
  • 100 Hz
Following figure shows an ac generator connected to a \ block box\ through a pair of terminals. The box contains possible R, L, C or their combination, whose elements and arrangements are not known to us. Measurements outside the box reveals that
e = 75 sin (sin ωt) volts, i = 1.5 sin (ωt+ 45° )
amp. The wrong statement is
Physics-Alternating Current-61966.png
  • There must be a capacitor in the box
  • There must be an inductor in the box
  • There must be a resistance in the box
  • The power factor is 0.707

Physics-Alternating Current-61967.png
  • 0.5 henry
  • 0.03 henry
  • 0.05 henry
  • 0.01 henry
If A and B are identical bulbs, which bulb glows brighter
Physics-Alternating Current-61969.png
  • A
  • B
  • Both equally bright
  • Cannot say
A series R–C circuit is connected to ac voltage source. Consider two cases; (A) when C is without a dielectric medium and (B) when C is filled with dielectric of constant 4. The current IRthrough the resistor and voltage VC, across the capacitor are compared in the two cases. Which of the following is/are true

  • Physics-Alternating Current-61971.png
  • 2)
    Physics-Alternating Current-61972.png

  • Physics-Alternating Current-61973.png

  • Physics-Alternating Current-61974.png
  • Both (and (3)
In the given circuit, the ac source has ω = 100 rad/s. considering the inductor and capacitor to be ideal, the correct choice (s) is (are)
Physics-Alternating Current-61976.png
  • The current through the circuit, I is 0.316 A
  • The current through the circuit, I is 0.3√2 A
  • The voltage across 100 Ω resistor = 10√2 V
  • The voltage across 50 Ω resistor = 10 V
  • Both (and (3)
In the given circuit the capacitor (C) may be charged through resistance R by battery V by closing switch S1. Also when S1is opened and S2is closed the capacitor is connected in series with inductor (L)
Given that the total charge stored in the LC circuit is Q0for t ≥ 0. The charge on the capacitor is
Physics-Alternating Current-61978.png

  • Physics-Alternating Current-61979.png
  • 2)
    Physics-Alternating Current-61980.png

  • Physics-Alternating Current-61981.png

  • Physics-Alternating Current-61982.png
In the given circuit the capacitor (C) may be charged through resistance R by battery V by closing switch S1. Also when S1is opened and S2is closed the capacitor is connected in series with inductor (L)
When the capacitor gets charged completely, S1is opened and S2is closed. Then
Physics-Alternating Current-61984.png
  • At t = 0, energy stored in the circuit is purely in the form of magnetic energy
  • At any time t > 0, current in the circuit is in the same direction
  • At t > 0, there is no exchange of energy between the inductor and capacitor
  • At any time t > 0 instantaneous current in the circuit may be
    Physics-Alternating Current-61985.png
In the given circuit the capacitor (C) may be charged through resistance R by battery V by closing switch S1. Also when S1is opened and S2is closed the capacitor is connected in series with inductor (L)
At the start, the capacitor was uncharged. When switch S1is closed and S2is kept open, the time constant of this circuit is τ. Which of the following is correct
Physics-Alternating Current-61987.png

  • Physics-Alternating Current-61988.png
  • After time interval 2τ, charge on the capacitor of
    Physics-Alternating Current-61989.png
  • The work done by the voltage source will be half of the heat dissipated when the capacitor is fully charge
  • After time interval 2τ, charge on the capacitor is
    Physics-Alternating Current-61990.png
You are given many resistances, capacitors and inductors. These are connected to a variable dc voltage source (the first two circuits) or an ac voltage source of 50 Hz frequency (the next three circuits) in different ways as shown in Column-II. When a current I (steady state for dc or r.m.s. for ac) flows through the circuit, the corresponding voltage V1 and V2 (indicated in circuits) are related as shown in Column-I. Match the two
Physics-Alternating Current-61992.png
  • A→ r, s, t ;B→q,r,s,t ;C→p,q ;D→q,r,s,t
  • A→ r, s ;B→q,r,t ;C→p,q ;D→q,s,t
  • A→ s, t ;B→r,s,t ;C→p,q ;D→q,r,s
  • A→ r, s ;B→q,s,t ;C→p,q ;D→r,s,t
The potential difference V and the current i flowing through an instrument in an ac circuit of frequency f are given by V = 5 cos ωt volts and I = 2 sin w t amperes (where ω = 2πf). The power dissipated in the instrument is
  • Zero
  • 10 W
  • 5 W
  • 2.5 W

Physics-Alternating Current-61996.png
  • 104 watt
  • 10 watt
  • 2.5 watt
  • 5 watt
The resistance of a coil dc is in ohms. In ac, the resistance
  • Will remain same
  • Will increase
  • Will decrease
  • Will be zero
Power dissipated in an LCR series circuit connected to an ac source of emf E is

  • Physics-Alternating Current-62000.png
  • 2)
    Physics-Alternating Current-62001.png

  • Physics-Alternating Current-62002.png

  • Physics-Alternating Current-62003.png
A generator produces a voltage that is given by V = 240 sin 120 t, where t is in seconds. The frequency and r.m.s. voltage are
  • 60 Hz and 240 V
  • 19 Hz and 120 V
  • 19 Hz and 170 V
  • 75 Hz and 70 V
The peak value of 220 volts of ac mains is
  • 155.6 volts
  • 220.0 volts
  • 311.0 volts
  • 440 volts
An ac generator produces an output voltage E = 170 sin 377 t volt, where t is in seconds. The frequency of ac voltage is
  • 50 Hz
  • 110 Hz
  • 60 Hz
  • 230 Hz

Physics-Alternating Current-62018.png
  • 20 watts
  • 40 watts
  • 1000 watts
  • 0 watt
In a circuit, the value of the alternating current is measured by hot wire ammeter as 10 ampere. Its peak value will be
  • 10 A
  • 20 A
  • 14.14 A
  • 7.07 A
In the transmission of ac power through transmission lines, when the voltage is stepped up n times, the powerloss in transmission
  • Increases n times
  • Decreases n times
  • Increases n2 times
  • Decreases n2 times
  • Decreases n4 times
An ac supply gives 30 V r.m.s. which passes through a 10 Ω resistance. The power dissipated in it is

  • Physics-Alternating Current-62022.png
  • 90 W

  • Physics-Alternating Current-62023.png
  • 45 W
The frequency of an alternating voltage is 50 cycles/sec and its amplitude is 120 V. Then the r.m.s. value of voltage is
  • 101.3 V
  • 84.8 V
  • 70.7 V
  • 56.5 V
In an ac circuit, the r.m.s. value of current, Irms is related to the peak current, I0 by the relation

  • Physics-Alternating Current-62026.png
  • 2)
    Physics-Alternating Current-62027.png

  • Physics-Alternating Current-62028.png

  • Physics-Alternating Current-62029.png
An alternating voltage is represented as E = 20 sin 300t. The average value of voltage over one cycle will be
  • Zero
  • 10 volt

  • Physics-Alternating Current-62030.png

  • Physics-Alternating Current-62031.png
The ratio of peak value and r.m.s. value of an alternating current is
  • 1
  • 2)
    Physics-Alternating Current-62032.png

  • Physics-Alternating Current-62033.png

  • Physics-Alternating Current-62034.png
If the value of potential in an ac circuit is 10 V, then the peak value of potential is

  • Physics-Alternating Current-62035.png
  • 2)
    Physics-Alternating Current-62036.png

  • Physics-Alternating Current-62037.png

  • Physics-Alternating Current-62038.png
A lamp consumes only 50% of peak power in an ac circuit. What is the phase difference between the applied voltage and the circuit current

  • Physics-Alternating Current-62040.png
  • 2)
    Physics-Alternating Current-62041.png

  • Physics-Alternating Current-62042.png

  • Physics-Alternating Current-62043.png
The instantaneous voltage through a device of impedance 20 Ω is e = 80 sin 100 πt. The effective value of the current is
  • 3 A
  • 2.828 A
  • 1.732 A
  • 4 A
Time constant of LC circuit is

  • Physics-Alternating Current-62046.png
  • 2)
    Physics-Alternating Current-62047.png

  • Physics-Alternating Current-62048.png

  • Physics-Alternating Current-62049.png
The phase angle between e.m.f. series ac circuit is LCR series ac circuit is

  • Physics-Alternating Current-62050.png
  • 2)
    Physics-Alternating Current-62051.png

  • Physics-Alternating Current-62052.png
  • π
An alternating current of frequency ‘f\' is flowing in a circuit containing a resistance R and a choke L in series.The impedance of this circuit is

  • Physics-Alternating Current-62067.png
  • 2)
    Physics-Alternating Current-62068.png

  • Physics-Alternating Current-62069.png

  • Physics-Alternating Current-62070.png
An inductance of 1 mH a condenser of 10 μF and a resistance of 50 Ω are connected in series. The reactances of inductor and condensers are same. The reactance of either of them will be
  • 100 Ω
  • 30 Ω
  • 3.2 Ω
  • 10 Ω
An alternating voltage E = 200√2 sin (100 t)is connected to a 1 microfarad capacitor through an ac ammeter. The reading of the ammeter shall be
  • 10 mA
  • 20 mA
  • 40 mA
  • 80 mA
The average power dissipation in a pure capacitance in ac circuit is

  • Physics-Alternating Current-62077.png
  • 2)
    Physics-Alternating Current-62078.png

  • Physics-Alternating Current-62079.png
  • Zero
In a region of uniform magnetic induction B =10–2tesla, a circular coil of radius 30 cm and resistance π2 ohm is rotated about an axis which is perpendicular to the direction of B and which forms a diameter of the coil. If the coil rotates at 200 rpm the amplitude of the alternating current induced in the coil is
  • 4 π2 mA
  • 30 mA
  • 6 mA
  • 200 mA
An inductive circuit contains a resistance of 10 ohm and an inductance of 2.0 henry. If an ac voltage of 120 volt and frequency of 60 Hz is applied to this circuit, the current in the circuit would be nearly
  • 0.32 amp
  • 0.16 amp
  • 0.48 amp
  • 0.80 amp
A 10 ohm resistance, 5 mH coil and 10 μF capacitor are joined in series. When a suitable frequency alternating current source is joined to this combination, the circuit resonates. If the resistance is halved, the resonance frequency
  • Is halved
  • Is doubled
  • Remains unchanged
  • In quadrupled
In a series circuit R = 300 Ω, L = 0.9 H, C = 2.0µF and ω = 1000 rad/sec. The impedance of the circuit is
  • 1300 Ω
  • 900 Ω
  • 500 Ω
  • 400 Ω
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