CBSE Questions for Class 12 Medical Physics Alternating Current Quiz 10 - MCQExams.com

A coil of $$10^{-2}\ H$$ inductance carries a current $$I=2\sin (100t)A$$. When current is half of its peak value then at that instant the induced emf in coil :-
  • $$1V$$
  • $$\sqrt{2}\ V$$
  • $$\sqrt{3}\ V$$
  • $$2V$$
Current in resistance is $$A$$, then
1082493_f5bfe194297948efa647c5fd4277ecae.png
  • $$V_{s}=15\ V$$
  • impedance of network is $$15\ Omega$$
  • power factor of given circuit is $$(0.46)$$ lagging (current is lagging)
  • NONE of the above
If $$\omega_t$$ and $$\omega_2$$ are half power frequencies of a series $$LCR$$ circuit, then resonant frequency $$\omega$$, can be expressed as :
  • $$\omega_r = \dfrac{\omega_1+\omega_2}{2}$$
  • $$\omega_r=\sqrt{\omega_1\omega_2}$$
  • $$\omega_r= \sqrt{\dfrac{\omega_1^2+\omega_2^2}{2}}$$
  • $$\omega_r = \dfrac{\omega_1\omega_2}{\omega_1+\omega_2}$$
In the given circuit, the $$AC$$ source has $$\omega=100\ rad/s$$. Considering the inductor and capacitor to be ideal, the correct choice(s) is(are)
1080246_47e81874072e4e57b15776487bb765c0.png
  • The current through the circuit, $$I$$ is $$0.3\ A$$
  • The current through the circuit, $$I$$ is $$0.3\sqrt {2}\ A$$
  • The voltage across $$100\Omega $$ resistor $$10\sqrt {2}V$$
  • The voltage across $$50\Omega $$ resistor $$10\ V$$
Rms value of current $$i = 3 + 4\sin \left( {\omega t + \frac{\pi }{3}} \right)$$ is:
  • $$5A$$
  • $$\sqrt {17} A$$
  • $$\frac{5}{{\sqrt 2 }}A$$
  • $$\frac{7}{{\sqrt 2 }}A$$
If an alternating current $$i=i_{m} \sin \omega t$$ is flowing through a capacitor then voltage drop $$\Delta V_{C}$$ across capacitor $$C$$ will be?
  • $$-\dfrac{i_{m}}{\omega C} \sin \omega t$$
  • $$-\dfrac{i_{m}}{\omega C} \cos \omega t$$
  • $$-\dfrac{i_{m}}{\omega C}\left(\sin \omega t +\dfrac{\pi}{4} \right)$$
  • $$\dfrac{i_{m}}{\omega C}\left(\sin \omega t -\dfrac{\pi}{4} \right)$$
In the given circuit the potential difference across resistance is $$54\ V$$ and power consumed by it is $$16\ W$$. If $$AC$$ frequency is $$60Hz$$ find the value of $$L$$:-
1093677_a3c6a220266241328c15d4240e5a1771.png
  • $$1\ H$$
  • $$2\ H$$
  • $$5\ H$$
  • $$4\ H$$
The resistance $$R = 10\Omega$$, inductance L = 2 mH and capacitance $$c of 5 \mu F$$ are connected in same to an AC source of frequency 50 Hz, then at resonance the impedance of circuit is
  • zero
  • $$10\Omega$$
  • $$1000\Omega$$
  • $$10k\Omega$$
Which of the shown graphs may represent the reactance of a series L-C combination?
In a series circuit, $$R=300 \Omega, L=0.9 H,C=2.0 \mu F$$ and $$\omega=1000 rad/s$$. The impedance of the circuit is 
  • $$1300 \Omega$$
  • $$900 \Omega$$
  • $$500 \Omega$$
  • $$400 \Omega$$
Two inductors $$L_{1}$$ and $$L_{1}$$ are connected in parallel and a time varying current $$i$$ flows as shown. The ratio of current $$i_{1}/i_{2}$$ at any time $$t$$ is
1129237_57c717abfd564aad82ac249b61f9d1a1.png
  • $$\dfrac{L_{2}}{L_{1}}$$
  • $$\dfrac{L_{1}}{L_{2}}$$
  • $$\dfrac{L_{1}^{2}}{(L_{1}+L_{2})^{2}}$$
  • $$\dfrac{L_{2}^{2}}{(L_{1}+L_{2})^{2}}$$
In given LCR circuit, the voltage across the terminals of a resistance and current will be -
1118361_0ecd6d974e9641dfb31d10c39927e8bd.png
  • $$400V,2A$$
  • $$800V,2A$$
  • $$100V,2A$$
  • $$100V,4A$$
An alternative current, L.R circuit comprises of an inductor, whose reactance $$X_L = 3R$$, where $$R$$ is the resistance of the circuit. If a capacitor, whose reactance $$X_C = R$$ is connected in series then what will be the ratio of the new and the old power factor?
  • $$\sqrt{2}$$
  • $$\dfrac{1}{\sqrt{2}}$$
  • $$2$$
  • $$1$$
The given graph shows volume with time in the source voltage and steady state current drawn by a series $$BLC$$ circuit:-
Which of the following statements is/are correct?
(a) Current lags the voltage.
(b) Resistance in the circuit is $$250\sqrt{\Omega}$$.
(c) Reactance in the circuit is $$250\Omega$$.
(d) Average power dissipation in the circuit is $$20\sqrt{3\Omega}$$
1130656_92b0e1e7e53f4d9daebf067ad5ac55e9.png
  • Only a
  • a & b
  • a, b & c
  • All
If the frequency of the AC source connected across a series LCR circuit is continuously in which the following is observed. Assume all other parameters are kept the same.
  • rms current continously increases.
  • rms current remains constant.
  • rms current first increases, reaches a maximum and then decrease.
  • rms current first decreases, reached a minimum and then increases.
In the adjoining figure the impedance of the circuit will be_
1118871_145a3a283ca44ee8af0e25ec77b15177.PNG
  • $$120\Omega$$
  • $$50\Omega$$
  • $$60\Omega$$
  • $$90\Omega$$
An inductance of $$1mH$$, a condenser of $$10 \mu F$$ and resistance of $$50\Omega$$ are connected in series. The reactance of inductor and condensers are same. The reactance of either of them will be:-
  • $$100 \Omega$$
  • $$30 \Omega$$
  • $$3.2 \Omega$$
  • $$10 \Omega$$
The graph given below depict the dependence of two reactive impedances $$X_1$$ and $$X_2$$ on the frequency of the alternating e.m.f. applied individually to them. We can say that:
1163690_35bffad96d6d48f7985b9e2bb090c749.png
  • $$X_1$$ is an inductor and $$X_2$$ is a capacitor
  • $$X_1$$ is a resistor and $$X_2$$ is a capacitor
  • $$X_1$$ is a capacitor and $$X_2$$ is an inductor
  • $$X_1$$ is an inductor and $$X_2$$ is a resistor
An AC circuit draws $$5 A$$ at $$160 V$$ and the power consumption is $$600 W$$. Then the power factor us :-
  • 1
  • 0.75
  • 0.50
  • Zero
An inductor of inductance 2.0 mH is connect across a charge capacitor of capacittance 5.0 uF , and the resulting LC circuit is set oscillating at natural frequency. Let Q denote the instantaneous charge on the capacitor, and I the current in the circuit. It is found the maximum value of Q is 200 uC .When Q=100uC the value of $$\dfrac{dI}{dt} $$ is found to be $$10^{x}$$ A/s. Find the value of x is then
  • x=-4
  • x=-5
  • x=4
  • x=5
A coil has a resistance $$ 10 \Omega $$ and an inductance of 0.4 henry. It is connected to an AC source of $$ 6.5 V , \frac {30} { \pi } Hz. $$ The average power consumed in the circuit, is :
  • $$ \cfrac {5} { 8} W $$
  • $$ \cfrac {4} {3} W $$
  • $$ \cfrac {3} {8} W $$
  • $$ \cfrac {6} {7} W $$
The inductive reactance of an inductive coil with $$\dfrac{1}{\pi}$$ henry and $$50$$Hz:-
  • $$\dfrac{50}{\pi}ohm$$
  • $$\dfrac{\pi}{50}ohm$$
  • 100 ohm
  • 50 ohm
In an electric circuit applied ac emf is e = 20 sin 300t volt and the current is i = 4 sin 300 t ampere. The reactance of the circuit is -
  • 5 ohm
  • 80 ohm
  • $$1.8 k\Omega $$
  • zero
In the given circuit, the potential difference across the $$6 \mu F$$ capacitor in steady state is 
1195021_694c8f0b8f73426294d338ad2e7e43ac.png
  • $$1\ V$$
  • $$6\ V$$
  • $$3\ V$$
  • $$4\ V$$
In general in an alternating current circuit for a complete cycle
  • The average value of current is zero
  • The average value of square of the current is zero
  • Average power dissipation is zero
  • All of these
The natural frequency of an LC circuit is 125 kHZz. when the capacitor is totally filled with a dielectric material, the natural frequency decreases by 25 kHz. Dielectric constant of the material is nearly. 
  • 3.33
  • 2.12
  • 1.56
  • 1.91
The impedance of coaxial cable, when its inductance is 0.40 $$\mu H$$ and capacitance is 1$$\times { 10 }^{ -11 }$$ F can be 
  • $$2\times { 10 }^{ 2 }{ \Omega }$$
  • 100$$\Omega $$
  • $$3\times { 10 }^{ 3 }{ \Omega }$$
  • $$3\times { 10 }^{ -2 }{ \Omega }$$
A capacitor is connected to an A.C generator.The ratio of reactance and impedance of capacitor is-
  • 1
  • Less than 1
  • greater than 1
  • zero
When induced emf in inductor coil is $$50%$$ of its maximum value then stored energy in inductor coil in the given circuit will be-
1170725_91a23ea2848e4bc6a96e85b4e2feadc9.png
  • $$2.5 \,mJ$$
  • $$5 \,mJ$$
  • $$15 \,mJ$$
  • $$20 \,J$$
Even if a physical quantity depends upon three quantites,out of which two are dimensionally same, then the formula cannot be derived by the method of dimensions.This statement.
  • may be true
  • may be false
  • must be true
  • must be false
An inductive circuit contains resistance of 10 ohms and an inductance of 20 H. If an A.c voltage of 120 volt and frequency 60 Hz is applied to this circuit , the current would be nearly
  • $$0.16 amp$$
  • $$0.3 amp$$
  • $$0.48 amp$$
  • $$0.80 amp$$
The alternating current in a circular is described by the graph as shown in figure. The rms current obtained from the graph would be 
1280131_c89428f7a4c34003ab61d4093f2ea2d7.png
  • 1.4 A
  • 2.2 A
  • 1.6 A
  • 2.6 A
A source of 220V is applied in an A.C. circuit. The value of resistance is $$220 \Omega$$. Frequency & inductance are 50 Hz and 0.7 H, then wattless current is 
  • $$0.5 amp$$
  • $$0.7 amp$$
  • $$1.0 amp$$
  • none
An alternating emf of angular frequency $$\omega $$ is applied across an inductance. The instantaneous power developed in the circuit has an angular frequency : 
  • $$\dfrac{\omega}{4 }$$
  • $$\dfrac{\omega}{2} $$
  • $$\omega $$
  • $$2\omega $$
Let $$\ell, r, c$$ and $$v$$ represent inductance, resistance, capacitance and voltage, respectively. The dimension of $$\dfrac{\ell}{rcv}$$ is $$SI$$ units will be:
  • $$[LTA]$$
  • $$[LA^{-2}]$$
  • $$[A^{-1}]$$
  • $$[LT^2]$$
For LCR series resonant circuit_______
  • impedence is maximum and current is minimum
  • impedence is minimum and current is maximum
  • impedence is minimum and current is minimum
  • impedence is maximum and current is maximum
The three lowest consecutive resonant frequency of a system are 50 Hz, 150 Hz and 250 Hz. The system could be
  • a tube of air closed at both ends
  • a tube of air open at one end
  • a tube of air open at both ends
  • a vibrating with fixed ends
An $$LCR$$ circuit is connected to a voltage source $$V_c$$ whose frequency can be varied. The frequency at which the voltage across the resistor is maximum, is 
  • $$902$$ $$Hz.$$
  • $$143$$ $$Hz.$$
  • $$23$$ $$Hz.$$
  • $$345$$ $$Hz.$$
When 100 volt DC source is applied across a coil, a current of 1 A flows through it. When 100 V AC source of 50 Hz is applied to the same coil, only 0.5 A current flows. Calculate the inductance of the coil.
  • $$(\pi/\sqrt{3})H$$
  • $$(\sqrt{3}/\pi)H$$
  • $$(2/\pi)H$$
  • None of these
In the given figure the impedance of the circuit will be
1266363_d31fe2dc8cc046ad8c2ede15ae2e4fda.png
  • $$120ohm$$
  • $$50ohm$$
  • $$60ohm$$
  • $$90ohm$$
In an LCR  circuit $$ R=100 \Omega $$ when capacitance C is removed, the current lags behind the voltage by $$ \pi / 3 $$. when inductance L is removed, the current leads the voltage by $$ \pi / 3 $$. the imoedance of the circuit is
  • 50 ohm
  • 100 ohm
  • 200 ohm
  • 400 ohm
In the only capacitive circuit, A.C voltage is 
  • leading by $$\pi$$
  • lagging behind by $$\pi$$
  • lagging behind by $$\pi/2$$
  • leading by  $$\pi/2$$
A generator with an adjustable frequency of oscillation is connect to resistance . $$R=100\Omega $$ inductance $${ L }_{ 1 }=1.7\quad mL\quad and\quad { L }_{ 2 }=2.3\quad mH\quad a$$ and capacitance , $${ C }_{ 1 }=\quad 4\mu F,\quad { C }_{ 2 }=2.5\mu F$$ and $${ C }_{ 3 }=3.5\mu F$$ . The resonant angular frequency of the circuit is 

1361768_35d28947dab546468f473cc18250c44a.png
  • 0.5 rad/s
  • $$0.5\times { 10 }^{ 4 }\quad rad/s$$
  • 2 rad/s
  • $$2\times { 10 }^{ -4 }\quad rad/s$$
If $$L$$ denotes the inductance of an inductor through which a current $$I$$ is flowing, then the dimensional formula of $$LI^2$$ is 
  • $$[MLT^{-2}]$$
  • $$[ML^2T^{-2}]$$
  • $$[M^2L^2T^{-2}]$$
  • not expressible in terms of $$M.L.T.$$
In the circuit shown how soon will the coil current reach $$\eta$$ fraction of the steady - state value 
1457373_38b6461e0fcc406584ba554fafe28b57.png
  • $$\frac { L } { R }$$
  • $$\frac { L } { R } \ln \frac { \eta } { ( 1 - \eta ) }$$
  • $$\frac { L } { R } \ln \frac { 1 } { ( 1 - \eta ) }$$
  • $$\frac { L } { R } \ln ( 1 - \eta )$$
In an A.C. circuit a capacitor of $$1 \mu F$$ value is connected to a source of frequency 1000 rad/sec. The value of capacitive reactance will be 
  • $$10 \Omega$$
  • $$100 \Omega$$
  • $$1000 \Omega$$
  • $$10,000 \Omega$$
The reactance of a coil when used in the domestic AC power supply (220 V 50 cycles) is 100 Ohm. The self inductance of the coil is nearly 
  • 3.2 Henry
  • 0.32 Henry
  • 2.2 Henry
  • 0.22 Henry
The rms speed of molecules of a gas is 200 m/s at $$27 ^ { \circ } C$$ and 1 atmosphere pressure.The rms speed at $$127 ^ { \circ } C$$ and double pressure is
  • $$\sqrt { \dfrac { 800 } { 3 } m }$$
  • $$\dfrac { 100 \sqrt { 2 } } { 3 } m / s$$
  • $$\dfrac { 400 } { \sqrt { 3 } } m / s$$
  • $$\dfrac { 800 } { 3 } m / s$$
Equivalent inductance of the circuit shown in the figure is
1428502_a95242c783554beabfd113edf9daeea3.png
  • $$1.0 H$$
  • $$1.75 H$$
  • $$0.75 H$$
  • $$0.25 H$$
Above the resonant frequency,
  • the frequency of the body is less than the frequency of the external periodic force.
  • the frequency of the body is greater than the frequency of the external periodic force.
  • the frequency of the body is exactly equal to the frequency of the external periodic force.
  • both (A) and (B)
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