JEE Questions for Physics Alternating Current Quiz 4 - MCQExams.com

A resistor R, an inductor L and a capacitor C are connected in series to an oscillator of frequency n. If the resonant frequency is nr, then the current lags behind voltage, when
  • n = 0
  • n < nr
  • n = nr
  • n > nr
The instantaneous values of current and voltage in an ac circuit are i = 100 sin 314 t amp and e = 200 sin (314 t + π/3)V respectively. If the resistance is 1Ω, then the reactance of the circuit will be

  • Physics-Alternating Current-61513.png
  • 2)
    Physics-Alternating Current-61514.png

  • Physics-Alternating Current-61515.png

  • Physics-Alternating Current-61516.png
The phase difference between the voltage and the current in an ac circuit is π/4. If the frequency is 50 Hz then this phase difference will be equivalent to a time of
  • 0.02 s
  • 0.25 s
  • 2.5 ms
  • 25 ms

Physics-Alternating Current-61519.png
  • ̶ π/6 rad
  • ̶ π/3 rad
  • π/6 rad
  • π/3 rad

Physics-Alternating Current-61521.png
  • The circuit is at resonance and its impedance is made up only of a reactive part
  • The current in the circuit is in phase with the applied e.m.f. and the voltage across R equals the applied e.m.f.
  • The sum of the p.d.'s across the inductance and capacitance equals the applied e.m.f. which is 180° ahead of phase of the current in the circuit
  • The quality factor of the circuit is ωL/R or 1 /ωCR and this is a measure of the voltage magnification (produced by the circuit at resonance) as well as the sharpenss of resonance of the circuit
  • Both (and (4)
In an ac circuit, the power factor
  • Is zero when the circuit contains an ideal resistance only
  • Is unity when the circuit contains an ideal resistance only
  • Is zero when the circuit contains an ideal inductance only
  • Is unity when the circuit contains an ideal inductance only
  • Both (and (3)

Physics-Alternating Current-61522.png
  • 4
  • 12
  • 15
  • 7
If L, C and R denote the inductance, capacitance and resistance respectively, then the dimensional formula for C2LR is
  • [ML-2T-1I0]
  • [M0L0T3I0]
  • [M-1L-2T6I2]
  • [M0L0T0I0
A series L–C–R circuit contains inductance 5 mH, capacitance 2μF and resistance 10Ω . If a frequency AC source is varied, what is the frequency at which maximum power is dissipated?

  • Physics-Alternating Current-61525.png
  • 2)
    Physics-Alternating Current-61526.png

  • Physics-Alternating Current-61527.png

  • Physics-Alternating Current-61528.png
Find the order of root mean square (rms) velocity of molecules of gas, if the velocity of sound in the same gas is 330 m/s. (γ = 1.
  • 481 m/s
  • 293 m/s
  • 280 m/s
  • 260 m/s
A series R–L–C circuit, driven with E rms = 120 V at frequency 50 Hz, contains an inductance with X L =100 Ω, a capacitance with XC =110Ω and an unknow resistance R. For what value of R, the power factor is 0.9?
  • 20Ω
  • 42Ω
  • 59Ω
  • 110Ω
A capacitor .50g is connected to a power source V = 220 sin 50t (V in volt, t in second). The value of rms current (in ampere)

  • Physics-Alternating Current-61532.png
  • 0.55 A

  • Physics-Alternating Current-61533.png

  • Physics-Alternating Current-61534.png
An emf of 15 V is applied in a circuit containing 5 H inductance, 10Ω resistance. The ratio of currents at time t = ∞ and t = 1 is

  • Physics-Alternating Current-61536.png
  • 2)
    Physics-Alternating Current-61537.png

  • Physics-Alternating Current-61538.png

  • Physics-Alternating Current-61539.png
In the given circuit, the AC source has co = 100 rad /s. Considering the inductor and capacitor to be ideal, the correct choice(s) is (are)
Physics-Alternating Current-61541.png
  • The current through the circuit, I is 0.3 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

Physics-Alternating Current-61543.png
  • 10 mA
  • 20 mA
  • 40 mA
  • 80 mA

Physics-Alternating Current-61545.png
  • 5.0 W
  • 2.5 W
  • 1.25 W
  • zero
The instantaneous voltage through a device of impedance 20 Ω is e = 80 sin 100πt. The effective value of the current is
  • 3 A
  • 2.828 A
  • 1.732 A
  • 4 A

Physics-Alternating Current-61548.png
  • 10 V
  • 5√3 V
  • 5 V
  • 1 V
A circuit area 0.01 m2 is kept inside a magnetic field which is normal to its plane. The magnetic field changes from 2 T to 1 T in 1 ms. If the resistance of the circuit is 2Ω. The amount of heat evolved is
  • 0.05 J
  • 50 J
  • 0.50 J
  • 500 J
The time taken by AC of 50 Hz in reaching from zero to the maximum value is
  • 50 × 10-3 s
  • 5 × 10-3 s
  • 1 × 10-3 s
  • 2 × 10-3 s
The average power dissipated in AC circuit is 2 W. If a current flowing through a circuit is 2 A impedance is 1Ω, what is the power factor of the AC circuit?
  • 0.5
  • 1
  • zero
  • 1/√2
If VAB =VAc, then X is
Physics-Alternating Current-61553.png
  • in resonance with inductance and capacitance
  • in resonance with resistance and capacitance
  • in resonance with inductance and resistance
  • None of the above
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 IR through the resistor and voltage VC across the capacitor are compared in the two cases. Which of the following is/are true?

  • Physics-Alternating Current-61554.png
  • 2)
    Physics-Alternating Current-61555.png

  • Physics-Alternating Current-61556.png

  • Physics-Alternating Current-61557.png
In the L-C-R circuit shown, the impedance is
Physics-Alternating Current-61559.png
  • 500Ω
  • 300Ω
  • 100Ω
  • 200Ω
In a series L-C-R circuit R = 200 Ω and the voltage and the frequency of the main supply is 220V 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 L-C-R circuit is
  • 305 W
  • 210 W
  • zero
  • 242 W
Assertion (A) In a series R-L-C circuit the voltages across resistor, inductor and capacitor are 8 V, 16 V and 10 V respectively. The resultant emf in the circuit is 10 V.
Reason (R) Resultant emf of the circuit is given by the relation.
Physics-Alternating Current-61562.png
  • If both A and R are correct and R is the correct explanation of A
  • If both A and R are correct but R in not the correct explanation of A
  • If A is correct but R is incorrect
  • If A is. incorrect but R is correct
In a series resonant R-L-C circuit, the voltage across R is 100 V and the value of R =1000Ω.The capacitance of the capacitor is 2 × 10-6 F; angular frequency of AC is 200 rad s -1. Then the potential difference across the inductance coil is
  • 100 V
  • 40 V
  • 250 V
  • 400 V
A resistor of R = 6 Ω, an inductor of L =1H and a capacitor of C =17.36µF are connected in series with an AC source. Find the Q -factor.
  • 3.72
  • 40
  • 2.37
  • 80
The values of L, C and R for a circuit are 1H, 9F and 3 Ω. What is the quality factor for the circuit at resonance?
  • 1
  • 9

  • Physics-Alternating Current-61566.png

  • Physics-Alternating Current-61567.png

Physics-Alternating Current-61569.png
  • 200
  • 100
  • 50
  • 25

Physics-Alternating Current-61571.png
  • between 1 and 2
  • 2

  • Physics-Alternating Current-61572.png

  • Physics-Alternating Current-61573.png
An AC voltage source has an output of ∆V = (200V) sin 2πft. This source is connected to a 100 Ω resistor. The (μC) current in the resistance is
  • 1.41 A
  • 2.41 A
  • 3.41 A
  • 0.71 A
What is the charge stored by 11μ F as shown in the figure?
Physics-Alternating Current-61576.png
  • 2.33 μC
  • 3.33 μC
  • 1.33 μC
  • 4.33 μC
220 V, 50 Hz AC is applied to a resistor. The instantaneous value of voltage is

  • Physics-Alternating Current-61578.png
  • 2)
    Physics-Alternating Current-61579.png

  • Physics-Alternating Current-61580.png

  • Physics-Alternating Current-61581.png
An L-C circuit contains a 20 mH inductor and a 50 μF capacitor with an initial charge of 10 mC. The resistance of the circuit is negligible. Let the instant the circuit is closed be t = 0. At what time is the energy stored completely magnetic?
  • t = 0
  • t = 1.57 ms
  • t = 3.14 ms
  • t = 6.28 ms
In a series resonant circuit, the AC voltage across resistance R, inductor L and capacitor C are 5 V, 10 V and 10 V respectively. The AC voltage applied to the circuit will be
  • 10 V
  • 25 V
  • 5 V
  • 20 V
What is the average power dissipation in an ideal capacitor in AC circuit?
  • 2CV2
  • 1/2 CV2
  • Zero
  • CV2
Find the time required for a 50 Hz alternating current to become its value from zero to the rms value
  • 10.0 ms
  • 2.5 ms
  • 15.0 ms
  • 5.0 ms
What is the value of inductance L for which the current is a maximum in a series L-C-R circuit with C =10 μF and co=1000s-1?
  • 100 mH
  • 1 mH
  • Cannot be calculated unless R is known
  • 10 mH
The value of alternating emf E in the given circuit will be
Physics-Alternating Current-61588.png
  • 220 V
  • 140 V
  • 100 V
  • 20 V

Physics-Alternating Current-61590.png
  • 250 kHz
  • 25 kHz
  • 2.5 kHz
  • 25 MHz
  • 2.5 MHz
An alternating voltage e = 200 sin 100 t is applied to a series combination R = 30Ω and an inductor of 400 mH. The power factor of the circuit is
  • 0.01
  • 0.2
  • 0.05
  • 0.042
  • 0.6

Physics-Alternating Current-61593.png

  • Physics-Alternating Current-61594.png
  • 10 A

  • Physics-Alternating Current-61595.png

  • Physics-Alternating Current-61596.png
  • 5 A

Physics-Alternating Current-61598.png
  • 0.5 H
  • 2.25 H
  • 3.9 H
  • 1.0 H
In L-C-R series circuit, the resonance condition in terms of capacitive reactance (XC) and inductive reactance (X L) is
  • XC + X L = 0
  • X C = 0
  • X L = 0
  • XC – X L = 0
A voltage of peak value 283 V and varying frequency is applied to a series L-C-R combination in which R = 3 Ω, L =25 mH and C = 400μF. The frequency (in Hz) of the source at which maximum power is dissipated in the above, is
  • 51.5
  • 50.7
  • 51.1
  • 50.3
An electric bulb has a rated power of 50 W at 100 V. If it is used on an AC source 200 V, 50 Hz, a choke has to be used in series with it. The should have an inductance of
  • 0.1 mH
  • 1 mH
  • 0.1 H
  • 1.1 H

Physics-Alternating Current-61602.png
  • 100 Hz
  • 75 Hz
  • 60 Hz
  • 30 Hz
  • 50 Hz

Physics-Alternating Current-61604.png
  • 11.4 Ω, 17.5 A
  • 30.7 Ω, 6.5 A
  • 40.4 Ω, 5 A
  • 50 Ω, 4 A
  • 35 Ω, 6.5 A
The inductance of the oscillatory circuit of a radio station is 10 mH and its capacitance is 0.25 µF. Taking the effect of resistance negligible, wavelength of the broadcasted waves will be (velocity of light = 3.0 × 108 ms -1, π = 3.14)
  • 9.42 × 104 m
  • 18.8 × 104 m
  • 4.5 × 104 m
  • None of these
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