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CBSE Questions for Class 12 Medical Physics Alternating Current Quiz 9 - MCQExams.com

Figure shows a series LCR circuit connected to a variable frequency 230 V source.
The source frequency which drives the circuit in resonance is

943657_707e8492feae4ec1b4ac2e3a7e8a618b.png
  • 4 Hz
  • 5 Hz
  • 6 Hz
  • 8 Hz
A series LCR circuit with R = 22 Ω, L = 1.5 H and C = 40 μ F is connected to a variable frequency 220 V ac supply. When the frequency of the supply equals the natural frequency of the circuit, what is the average power transferred to the circuit in one complete cycle?
  • 2000 W
  • 2200 W
  • 2400 W
  • 2500 W
To reduce the resonant frequency in an LCR series circuit with a generator.
  • The generator frequency should be reduced
  • Another capacitor should be added in parallel to the first
  • The iron core of the inductor should be removed
  • Dielectric in the capacitor should be removed
An LC circuit contains a 20 mH inductor and a 50 .μ F capacitor with an initial charge of 10 mC. The resistance of the circuit is.negligible. Let the instant at which the circuit which is closed be t =At what time the energy stored is completely magnetic?
  • t = 0
  • t = 1.54 ms
  • t = 3.14 ms
  • t = 6.28 ms
In the given circuit, initially K1 is closed and K2 is open. Then K1 is opened and K2 is closed. If q1 and q2 are charges on C1 and C2 and V1 and V1 are the voltage respectively, then
945107_975ac49a546b45d9bc1eb3c90d83ac09.png
  • charge on C1 gets redistributed such that V1 = V2
  • charge on C1 gets redistributed such that q1 = q2
  • charge on C1 gets redistributed such that C1V1 = C2V2 = C1V
  • charge on C1 gets redistributed such that q1 + q2 = 2q
Two inductors of inductance L each are connected in series with opposite magnetic fluxes. The resultant inductance is (Ignore mutual inductance)
  • zero
  • L
  • 2L
  • 3L
A voltage of peak value 283 V and varying frequency is applied to series LCR combination in which R = 3Ω, L = 25 mH and C = 400μF. Then 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
The natural frequency(ω0) of oscillations in LC Circuit is given by:
  • 12π1LC
  • 1π12LC
  • 1LC
  • LC
A transmitter transmits at a wave length of 300 meters. A capacitor of a capacitance 9.6 μ F is being used. The value of the inductance for the resonant circuit is approximately
  • 2.5 mH
  • 2.5 μ H
  • 2.5 nH
  • 2.5 pH
A 50W,100V lamp is to be connected to an AC mains of 200V,50Hz. What capacitance is essential to be put in series with the lamp?
  • 9.2
  • 8
  • 10
  • 12
A source of constant voltage V is connected to a resistance R and two ideal inductors L_{1} and L_{2} through a switch S as shown. There is no mutual inductance between the two inductors. The switch S is initially open. At t=0, the switch is closed and current beings to flow. Which of the following options is/are correct?
1011243_8b0bf7a396db4ba0b9e7b7a7d7b20681.png
  • After a long time, the current through L_{1} will be \dfrac {V\ \ L_{2}}{R\ L_{1}+L_{2}}
  • After a long time, the current through L_{2} will be \dfrac {V\ \ L_{2}}{R\ L_{1}+L_{2}}
  • The ratio of the currents through L_{1} and L_{2} is fixed at all times (t\ >\ 0)
  • At t=0, the current through the resistance R is \dfrac {V}{R}
If R is resistance, L is inductance, C is capacitance, H is latent heat, and s is specific heat, then match the quantity given in Column I with the dimensions given in Column II.

Column IColumn II
i. LCa. MA^{-2}L^2T^{-2}
ii. LRb. ML^2T^{-3}A^{-2}
iii. Hc. T^2
iv. Rd. M^2L^4T^{-5}A^{-4}
  • i. c, ii.b, iii.a, iv.d
  • i. a, ii.d, iii.a, iv.b
  • i. c, ii.d, iii.a, iv.b
  • i. c, ii.d, iii.a, iv.d
A 100mH inductor, a 25\mu F capacitor and a 15\Omega resistor are connected in series to a 120V, 50Hz ac source. Calculate
(a) impedance of the circuit at resonance
(b) current at resonance
(c) resonant frequency
  • (a) 16\Omega  (b) 9A  (c) 100Hz
  • (a) 15\Omega  (b) 8A  (c) 100Hz
  • (a) 15\Omega  (b) 8A  (c) 120Hz
  • (a) 15\Omega  (b) 7A  (c) 100Hz
Find the maximum value of current when inductance of two henry is connected to 150V,50 cycle supply
  • \cfrac { 3 }{ 2\sqrt { 2 } A }
  • \cfrac { 5 }{ 2\sqrt { 2 } A }
  • \cfrac { 6 }{ 2\sqrt { 2 } A }
  • \cfrac { 7 }{ 2\sqrt { 2 } A }
A 10\Omega resistance, 5mH coil and 10\mu F 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
  • is quadrupled
A resistance (R)=12\Omega; inductance (L)=2 henry and capacitive reactance C=5mF are connected in series to an ac generator, then:
  • at resonance, the circuit impedance is zero
  • at resonance, the circuit impedance is 12\Omega
  • the resonance frequency of the circuit is 1/2\pi
  • at resonance, the inductive reactance is less than the capacitive reactance
Find the impedance of AC circuit at resonance shown in the adjacent figure.
1013650_0eca99fb9bea4ee1855cd5a8e7df6c24.png
  • 100\sqrt{2}\Omega
  • 200\Omega
  • 100\Omega
  • 200\sqrt{2}\Omega
An ac source of angular frequency \omega is fed across a resistor R and a capacitor C in series. The current registered is I. If now the frequency of source is changed to \omega/3 (but maintaining the same voltage), the current in the circuit is found to be halved. The ratio of reactance at the original frequency \omega will be:
  • \sqrt { \cfrac { 3 }{ 5 } }
  • \sqrt { \cfrac { 5 }{ 3 } }
  • 3/5
  • 5/3
Determine the characteristic impedance of a transmission line which has a capacitance of 35pF/ft and an inductance of 0.25\mu H/ft
  • 84.5
  • 95
  • 65
  • 66
In an LCR circuit having L=8.0H,C-0.5\mu F and R=100\Omega in series, the resonance frequency is:
  • 600 rad/sec
  • 600Hz
  • 500 rad/sec
  • 500Hz
The reciprocal of impedance is called
  • reactance
  • admittance
  • inductance
  • susceptance
In LCR circuit the capacitance is changed from C to 4C. For the same resonant frequency, the inductance should be changed from L to
1013627_2f195f38f4674dccbc01e95c165987f3.png
  • 2L
  • L/2
  • L/4
  • 4L
In a series LCR circuit K=200\ \Omega and the voltage and frequency of the main supply are 220\ V and 50\ Hz respectively. On taking out the capacitor from the circuit, the current leads the voltage by {30}^{o}. On taking out the indicator from the circuit the current leads the voltage by {30}^{o}. The power dissipated in the LCR circuit is :
  • 342\ W
  • 305\ W
  • 209\ W
  • 242\ W
In the series LCR circuit as shown in figure, the voltmeter and ammeter readings are:
1022295_e9edff30593046468140204fe0ae9b2c.png
  • V=100\ volt, I=2\ amp
  • V=100\ volt, I=5\ amp
  • V=1000\ volt, I=2\ amp
  • V=300\ volt, I=1\ amp
For series L-C-R AC circuit shown in figure, the readings of {V}_{2} and {V}_{3} are same and each equal to 100\ V. Then
1022792_47873930ffad4fc79c0e931fa23ad021.png
  • The reading {V}_{1} is 200\ V
  • The reading of {V}_{2} is 0
  • The circuit is in resonant mode 
  • The inductive and capacitive reactance are equal
The characteristic impedance of a co-axial cable is of order of:
  • 50\Omega
  • 200\Omega
  • 270\Omega
  • none of these
If instantaneous current in a circuit is given by l = (2 + 3 sin \omega t)A, then the effective value of resulting current in the circuit is:
  • \sqrt\frac{17}{2}A
  • \sqrt\frac{2}{17}A
  • \sqrt\frac{3}{\sqrt2}A
  • 3\sqrt2A
Which of the following option is correct for an ideal capacitor connected to a sinusoidal voltage source over a complete cycle?
  • Neither the average power nor the average current is zero
  • Average voltage is zero but the average power is non zero
  • Both the average power and average current is zero
  • Average power is zero, but the average current is non zero

A resistance of 10\Omega , a
capacitance of 0.1\mu F and an inductance of 2mH are connected in
series  across a source of alternating
emf of  variab frequency. At what frequency  does maximum current flow?

  • 11.25kHz
  • 23.76kHz
  • 35.46kHz
  • 46.72kHz
The frequancy of oscillation of current in the inductor is-
1024264_f0625ce816a340338372ed516ce6a3f0.png
  • \dfrac { 1 }{ 3\sqrt { LC } }
  • \dfrac {1}{6\pi \sqrt {LC}}
  • \dfrac { 1 }{\sqrt { LC } }
  • \dfrac {1}{2\pi \sqrt {LC}}
The equation of an alternating voltage is V=100\sqrt {2}\sin {100\pi t} volt. The RMS value of voltage and frequency will be respectively
  • 100V,50Hz
  • 50V,100Hz
  • 150V, 50Hz
  • 200V, 50Hz
An alternating power supply of 220 V is applied across a series circuit of resistance 10\sqrt{3}\Omega, capacitive reactance 40 \Omega and inductive reactance 30 \Omega. The respective current in the circuit for zero and infinite frequencies are
  • 2A,\dfrac{1}{2}A
  • 0A,10A
  • 10 A,0A
  • 0A,0A
A coil has resistance 30 \Omega and inductive reactance 20 \Omega at 50 Hz frequency.If an ac source of 200 V,100Hz is connected across the coil ,the current in the coil in the coil will be 
  • \dfrac{20}{\sqrt{13}}A
  • 2.0 A
  • 4.0A
  • 8.0A
Figure shows a long straight conductor carrying current i. A square loop of side a is kept at a distance r from it. Which of the following is correct?
1049863_410edb917c2e4b14bc58116e203aac45.png
  • Mutual Inductance M = \dfrac{\mu_0 a}{2 \pi} ln(1 + \dfrac{a}{r})
  • If loop is pulled with constant speed v along x-axis, emf induced at the instant is \dfrac{\mu_0 i a^2 v}{2 \pi r (r + a)}
  • If loop is pulled with constant speed v, no emf is induced
  • If i increases with time, the loop is replied away from the straight conductor.
A L - C resonant circuit contains a 200 pF capacitor and a 100 \mu H inductor it is set into oscillation coupled to an antenna. The wavelength of the radiated electromagnetic waves is
  • 377 mm
  • 266 m
  • 377 cm
  • 3.77 cm
In a series L-C circuit , if L= 10^{-3}H and C=3 \times 10^{-7} F  is connected to a 100V-50Hz a.c. source, the impedance of the circuit is 
  • \cfrac{10^5}{3\pi} - 10\pi
  • 0.1\pi - 3\times 10^{-5}\pi
  • \cfrac{10^5}{3\pi} - \cfrac{\pi}{10}
  • None of these
The sinusoidal potential difference V_1 shown in figure applied across a resistor R produces heat at a rate W. what is the rate of heat dissipation when the square waves potential different V_2 as shown in figure is applied across the resistor?
1066298_181d35a1d15f46ada01d542f7e12ebaf.png
  • \dfrac{W}{2}
  • W
  • \sqrt{2}W
  • 2W
In L-C-R series circuit consists of a resistance of 10 \Omega a capacitor of reactance 6.0 \Omega and an inductor coil. The circuit is found to resonate when put across a 300 V, 100 Hz supply. The inductance of coil is (Take \pi = 3)
  • 0.1 H
  • 0.01 H
  • 0.2 H
  • 0.02 H
In a series LCR circuit,the inductive reactance is twice the resistance and the capacitance reactance is {\frac{1}{3}^{rd}} the inductive reactance. The power factor of the circuit is:
  • 0.5
  • 0.6
  • 0.8
  • 1
For the series LCR circuit shown in the figure, what is the resonance frequency and the amplitude of the current at the resonating frequency.
1065954_a2a6adb45b7e4d8db91bd669a34185fd.png
  • 2500 rad s^{-1} and 5\sqrt 2 A
  • 2500 rad s^{-1} and 5A
  • 2500 rad s^{-1} and \frac{5}{\sqrt 2} A
  • 25 rad s^{-1} and 5\sqrt 2 A
In the LCR circuit shown in figure unknown resistance and alternating voltage source are connected. When switch 'S' is closed then there is a phase difference of \dfrac {\pi}{4} between current and applied voltage and voltage across resister is \dfrac {100}{\sqrt {2}}V. When switch is open current and applied voltage are in same phase. Neglecting resistance of connecting wire answer the following questions:
Resonance frequency of circuit is
1068875_ba7b7a96124147a2b554a100c567d0be.png
  • 50\ Hz
  • 25\ Hz
  • 75\ Hz
  • Data insufficient for calculation
In the L -C circuit shown in figure,the current is in direction shown in the figure and charges on the capacitor plates have sign shown in the figure A this time:-
1062889_d7fc6e9c09a04a07bf95b46310cac5c3.png
  • i as well as Q increasing
  • i as well as Q decreasing
  • i is increasing but Q is decreasing
  • i decreasing but Q is increasing
The voltage across a pure inductor is represented in figure. Which one of the following curves in the figure will represent the current?
1075123_44379ab393c44f4980b169eeef6b0d3b.PNG
A 2 F capacitor is initially charged to 20 V and then shorted across a 5 mH inductor. The angular frequency of oscillation is.
  • 1000 {rad/s}
  • 100 {rad/s}
  • 10000 {rad/s}
  • 10 {rad/s}
A inductance capacitance circuit is in the state of resonance. if the C = 0.1 \mu F and L = 0.25 Henry. Neglecting ohmic resistance of circuit what is the frequency of oscillations
  • 1007 \ Hz
  • 100 \ Hz
  • 109 \ Hz
  • 500 \ Hz
In a series LCR circuit 
V_l = 3V_R and V_C = 2V_R
Volatge across capacitance
1080236_a8d2ce61799d426d9a74ea65417ef0b9.png
  • 110 V
  • 220 V
  • 330 V
  • 440 V
In the given circuit the maximum current can be
1078282_11b166a0b7b34efab518327ebd9ade9b.png
  • \dfrac{E_0}{R}
  • \dfrac{E_0}{\omega L}
  • E_0\omega C
  • \frac{E_0}{\Bigg[ \Big\lgroup \omega L - \dfrac{1}{\omega C} \Big\rgroup^2 + R^2 \Bigg ]^{1/2}}
Impedance of the following circuit will be:
1092425_4f10561475c04e4e86256a25caa9d49d.png
  • 150\ \Omega
  • 200\ \Omega
  • 250\ \Omega
  • 340\ \Omega
In case of AC circuits, impedance is given by the ratio of
I. Peak values of voltage and current
II. rms values of voltage and current
III. Instantaneous values of voltage and current.
  • I only
  • II only
  • I and II
  • I, II and III
A loop is formed by two parallel conduction connected by a solenoid with inductance L = 10^3 H and a conducting rod of mass m=1 gm which can freely slide (without friction) over a pair of conductors. The conductors are located in a horizontal plane in a uniform magnetic field B = 4 T in the direction shown. The distance between conductors is equal to t = 1 m. At the moment t = 0 , the rod is imparted an initial velocity V_0 to the right. Determine angular frequency (in rad/s) of oscillation of rod.
  • 4
  • 6
  • 8
  • 10
0:0:3


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