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 $$\Omega$$, L = 1.5 H and C = 40 $$\mu$$ 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 .$$\mu$$ 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 $${ K }_{ 1 }$$ is closed and $${ K }_{ 2 }$$ is open. Then $${ K }_{ 1 }$$ is opened and $${ K }_{ 2 }$$ is closed. If $${ q }_{ 1 }^{ \prime  }$$ and $${ q }_{ 2 }^{ \prime  }$$ are charges on $${ C }_{ 1 }$$ and $${ C }_{ 2 }$$ and $${ V }_{ 1 }$$ and $${ V }_{ 1 }$$ are the voltage respectively, then
945107_975ac49a546b45d9bc1eb3c90d83ac09.png
  • charge on $${ C}_{ 1 }$$ gets redistributed such that $${ V }_{ 1 }$$ = $${ V }_{ 2 }$$
  • charge on $${ C}_{ 1 }$$ gets redistributed such that $${ q }_{ 1 }^{ \prime }$$ = $${ q }_{ 2 }^{ \prime }$$
  • charge on $${ C}_{ 1 }$$ gets redistributed such that $${ C }_{ 1 }{ V }_{ 1 }$$ = $${ C }_{ 2 }{ V }_{ 2 }$$ = $${ C }_{ 1 }V$$
  • charge on $${ C}_{ 1 }$$ gets redistributed such that $${ q }_{ 1 }^{ \prime }$$ + $${ q }_{ 2 }^{ \prime }$$ = 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 = 3$$\Omega$$, L = 25 mH and C = 400$$\mu$$F. 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$$ (\omega_0)$$ of oscillations in LC Circuit is given by:
  • $$ \dfrac{1}{2\pi}\dfrac{1}{\sqrt{LC}} $$
  • $$ \dfrac{1}{\pi}\dfrac{1}{\sqrt{2LC}}$$
  • $$ \dfrac{1}{\sqrt{LC}}$$
  • $$ \sqrt{LC} $$
A transmitter transmits at a wave length of 300 meters. A capacitor of a capacitance 9.6 $$\mu$$ F is being used. The value of the inductance for the resonant circuit is approximately
  • 2.5 mH
  • 2.5 $$\mu$$ 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.
  • $$4$$
  • $$6$$
  • $$8$$
  • $$10$$
0:0:1


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