JEE Questions for Physics Alternating Current Quiz 1 - MCQExams.com

Average power in the L–C–R circuit depends upon the
  • current
  • phase difference only
  • emf
  • current, emf and phase difference
In Colpitt oscillator the feedback network consists of
  • two inductors and a capacitor
  • two capacitors and an inductor
  • three pairs of R-C circuit
  • three pairs of R-L circuit
In a circuit, the current lags behind the voltage by a phase difference of π/ 2, the circuit will contains which of the following ?
  • Only R
  • Only C
  • R and C
  • Only L
A choke is preferred to a resistance for limiting current in AC circuit, because
  • choke is cheap
  • there is no wastage of power
  • choke is compact in size
  • choke is a good absorber of heat
In L-C-R circuit if resistance increases, quality factor
  • increases finitely
  • decreases finitely
  • remains constant
  • None of these
In an L-C-R series AC circuit, the voltage across each of the components L, C and R is 50 V. The voltage across the L-C combination will be
  • 50 V
  • 50√2 V
  • 100 V
  • zero
In an L-C-R circuit, capacitance is changed from C to 2C. For the resonant frequency to remain unchanged, the inductance should be changed from L to
  • 4L
  • 2L
  • L/2
  • L/4
In an AC circuit, the current lags behind the voltage by π/3. The components of the circuit are
  • R and L
  • L and C
  • R and C
  • Only R
An inductance 1 H is connected in series with an AC source of 220 V and 50 Hz. The inductive reactance (in ohm) is
  • 2 π
  • 50 π
  • 100 π
  • 1000 π
The current voltage relation of diode is given by I = (el000V/T –mA, where the applied voltage V is in volt and the temperature T is in kelvin. If a student makes an error measuring ± 0.01 V while measuring the current of 5 mA at 300 K, what will be the error in the value of current in mA?
  • 0.2 mA
  • 0.02 mA
  • 0.5 mA
  • 0.05 mA
The magnetic field in a travelling electromagnetic wave has a peak value of 20 nT. The peak value of electric field strength is
  • 3 V/m
  • 6 V/m
  • 9 V/m
  • 12 V/m
A hot wire ammeter reads 10 A in an AC circuit. The peak value of the current will be

  • Physics-Alternating Current-61332.png
  • 2)
    Physics-Alternating Current-61333.png

  • Physics-Alternating Current-61334.png

  • Physics-Alternating Current-61335.png

Physics-Alternating Current-61337.png
  • 22 mA
  • 33 mA
  • 42 mA
  • 12 mA
The peak value of an alternating current is 5 A and its frequency is 60 Hz. Find its rms value and time taken to reach the peak value of current starting from zero.
  • 3.536 A, 4.167 ms
  • 3.536 A, 15 ms
  • 6.07 A, 10 ms
  • 2.536 A, 4.167 ms
What is the average value of the AC voltage over one complete cycle?
  • zero
  • Vmax

  • Physics-Alternating Current-61340.png

  • Physics-Alternating Current-61341.png
A telephone wire of length 200 km has a capacitance of 0.014 μF per km. If it carries an AC frequency 5 kHz, what should be the value of an inductor required to be connected in series so that the impedance of the circuit is minimum?
  • 0.35 mH
  • 3.5 mH
  • 2.5 mH
  • zero
The maximum voltage in DC circuit is 282V.The effective voltage in AC circuit will be
  • 200 V
  • 300 V
  • 400 V
  • 564 V
Alternating current cannot be measured by DC ammeter because
  • AC cannot pass through DC ammeter
  • AC changes direction
  • average value of current for complete cycle is zero
  • DC ammeter will get damaged
An AC voltage source of variable angular frequency w and fixed amplitude V0, is 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 impedance of the circuit is unchanged
  • total impedence of the circuit increases
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
An ideal choke draws a current of 8 A when connected to an AC supply of 100 V, 50 Hz. A pure resistor draws a current of 10 A when connected to the same source. The ideal choke and the resistor are connected in series and then connected to the AC source of 150 V, 40 Hz. The current in the circuit becomes

  • Physics-Alternating Current-61347.png
  • 8 A
  • 18 A
  • 10 A
A 50 V AC is applied across an R-C (series) network. The rms voltage across the resistance is 40 V, then the potential across the capacitance would be
  • 10 V
  • 20 V
  • 30 V
  • 40 V
A pure inductive coil of 30 mH is connected to an AC source of 220 V, 50 Hz. The rms current in the coil is
  • 50.35 A
  • 23.4 A
  • 30.5 A
  • 12.3 A
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 emf of AC is increased, the effect on the value of the current
  • 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 maximum value of AC voltage in a circuit is 707 V. Its rms value is
  • 70.7 V
  • 100 V
  • 500 V
  • 707 V
If an alternating voltage is represented as E= 141 sin (628 t), then the rms value of the voltage and the frequency are respectively
  • 141 V, 628 Hz
  • 100 V, 50 Hz
  • 100 V, 100 Hz
  • 141 V, 100 Hz
In an ideal choke, ratio of its inductance L to its DC resistance R is
  • infinity
  • zero
  • unity
  • hundred
For a series L-C-R circuit at resonance, the statement which is not true, is
  • peak energy stored by a capacitor = peak energy stored by an inductor
  • average power = apparent power
  • wattless current is zero
  • power factor is one
In a choke coil, the reactance XL and resistance R are such that
  • XL = R
  • XL > > R
  • XL < < R
  • XL = ∞
A 100 V, AC source of frequency 500 Hz is connected to an L-C-R circuit with L= 8.1 mH C =12.5µF, R =10Ω all connected in series as shown in figure. What is the quality factor of circuit?
  • 2.02
  • 2.5434
  • 20.54
  • 200.54
In a L-C-R series circuit, the potential difference between the terminals of the inductance is 60 V, between the terminals of the capacitor is 30 V and that across the resistance is 40 V. Then, supply voltage will be equal to the
  • 50 V
  • 70 V
  • 130 V
  • 10 V
The natural frequency of an L-C circuit is 125000 cycle/s. Then the capacitor C is replaced by another capacitor with a dielectric medium of dielectric constant K. In this case, the frequency decreases by 25 kHz. The value of K is
  • 3.0
  • 2.1
  • 1.56
  • 1.7
Average power generated in an inductor connected to an AC source is
  • 1/2 Li2
  • Li2
  • zero
  • None of these
In a series L-C-R circuit, resistance R =10Ω and the impedance Z =10Ω. The phase difference between the current and the voltage is
  • 0°
  • 30°
  • 45°
  • 60°
A circuit consists of an inductance of 0.5 mH and a capacitor of 20 µF. The frequency of the L-C oscillations is approximately
  • 400 Hz
  • 88 Hz
  • 1600 Hz
  • 2400 Hz
An inductor is connected to an AC source. When compared to voltage, the current in the lead wires
  • Is ahead in phase by π
  • Lags in phase by π

  • Physics-Alternating Current-61361.png

  • Physics-Alternating Current-61362.png
A circuit has a resistance of 12 Ω and an impedance of 15 Ω. The power factor of the circuit will be
  • 0.8
  • 0.4
  • 1.25
  • 0.125
The phase difference between the alternating current and emf is π/2 . Which of the following cannot be the constituent of the circuit?
  • C alone
  • R, L
  • L, C
  • L alone
If the capacity of a condenser is 1 F, then its resistance in a DC circuit will be
  • zero
  • infinity
  • 1 Ω
  • 1/2 Ω
An L-C-R circuit of R =100Ω is connected to an AC source 100 V, 50 Hz. The magnitude of phase difference between current and voltage is 30°. The power dissipated in the L-C-R circuit is
  • 50 W
  • 86.6 W
  • 100 W
  • 200 W
The power factor of an AC circuit having resistance R and inductance L (connected in series) and an angular velocity ω is
  • R/ωL
  • R/(R2 + ω2 L2)1/2
  • ωL/R
  • R/(R2 – ω2 L2)1/2
An ac generator produces an output voltage E = 170 sin 377 t volts, where t is in seconds. The frequency of an voltage is
  • 50 Hz
  • 110 Hz
  • 60 Hz
  • 230 Hz
An installation consisting of an electric motor driving a water pump left 75 L of water per sec of a height of 4.7 m. If the motor consumes a power of 5 kW, then the efficiency of the installation is
  • 39%
  • 69%
  • 93%
  • 96%
An ideal transformer has 500 and 5000 turn in primary and secondary windings respectively. If the primary voltage is connected to a 6 V battery, then the secondary voltage is
  • zero
  • 60 V
  • 0.6 V
  • 6.0 V
A resistor and a capacitor are connected in series with an AC source. If the potential drop across the capacitor is 5 V, and that across resistor is 12 V, then applied voltage is
  • 13 V
  • 17 V
  • 5 V
  • 12 V
An ideal coil of 10 H is connected in series with a resistance of 5 Ω and a battery of 5 V. 2 s after the connection is made, the current flowing (in ampere) in the circuit is
  • (1 – e)
  • e
  • e-1
  • (1 – e-1)
A coil of inductance 300 mH and resistance 2 Ω is connected to a source of voltage 2V. The current reaches half of its steady state value in
  • 0.05 s
  • 0.1 s
  • 0.15 s
  • 0.3 s
A 4µF capacitor, a resistance of 2.5 m Ωis in series with 12 V battery. Find the time after which the potential difference across the capacitor is 3 times the potential difference across the resistor. (given, ln (= 0.
  • 13.86 s
  • 6.93 s
  • 7 s
  • 14 s
A coil is wound on an iron core and looped back on itself so that core has two sets of closely wound coils carrying currents in opposite directions. The self-inductance is
Physics-Alternating Current-61373.png
  • zero
  • 2L
  • 2L + M
  • 2L+ 2M
A movable wire is moved to the right causing an anticlock-wise induced current Fig. The direction of magnetic induction in the region P points
Physics-Alternating Current-61375.png
  • to the right
  • to the left
  • up the paper
  • down into the paper
0:0:1


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