CBSE Questions for Class 12 Medical Physics Alternating Current Quiz 14 - MCQExams.com

For the circuit shown in the figure the current through the inductor is $$1.6\ A$$ , while the current through the condenser is $$0.4\ A,$$ then the current $$l$$ drawn from the source is :
1110199_7c6f96e79e3146839aa95849a5b2af87.png
  • $$ 2 \sqrt{2}\ A$$
  • $$1.65\ A$$
  • $$1.2\ A$$
  • $$2.0\ A$$
A pure inductor $$I$$, a cpacitory $$C$$ and a resistance $$R$$ are connected across a battery of emf $$E$$ and internal resistance $$r$$ as shown in figure. Switch $${S}_{w}$$ is closed at $$t=0$$, select the correct alternative(s).
1105369_041d72398555422ab68bd70332ddeed7.PNG
  • current through resistance $$R$$ is zero all the time
  • current through resistance $$R$$ is zero at $$t=0$$ and $$t\rightarrow \infty$$
  • maximum charge stored in the capacitor is $$CE$$
  • maximum energy stored in the inductor is equal to the maximum energy stored in the capacitor
In the given AC circuit
1105698_3f5ad13f6c1c4821a221538f2ac954f6.png
  • current $$I_2$$ and V are is same phase
  • current $$I_2$$ leads $$I_1$$ by $$90^0$$
  • current I leads $$I_2$$ by $$\theta < 90^0$$
  • current I leads $$I_1$$ by $$\theta < 90^0$$
A LC circuit is in the state of resonance. if $$C=0.1 \ \mu F $$ and $$L = 0.25 \ henry.$$  Neglecting ohmic resistance of circuit what is the frequency of oscillations
  • 1007 Hz
  • 100 Hz
  • 109 Hz
  • 500 Hz
An alternating current of $$1.5mA$$ and angular frequency $$300\ rad/sec$$ flows through a $$10K\Omega $$ resistor and a $$0.50\mu F$$ capacitor in series. find the rms voltage across the capacitor and impedance of the circuit?
  • $$1.2\times 10^{4}\Omega ;\ 10V$$
  • $$10^{4}\Omega ;\ 10^{4}V$$
  • $$1.0\times 1.0^{4}\Omega ;\ 50V$$
  • $$10\Omega ;10v$$
A bulb is rated $$55 W/110 V$$. It is to be connected to a $$220 V/50 Hz$$ with inductor in series. The value inductance, so that bulb gets correct voltage is: 
  • $$220 \omega^{-1}$$
  • $$110 \omega^{-1}$$
  • $$377.5 \omega^{-1}$$
  • $$300 \omega^{-1}$$
Impedance of given circuit is Given: $$R = 1\ \Omega, C = \frac {5 \sqrt 2}{2 \pi} \times 10^{-2}\ F, L = \frac {1}{40 \pi}\ H$$, frequency of A.C. source = $$100\ Hz$$.
1220614_818d9cbd8500425783175d6595fa389f.jpg
  • $$1\ \Omega$$
  • $$2\ \Omega$$
  • $$\sqrt 2\ \Omega$$
  • $$2 \sqrt 2\ \Omega$$
An inductance of $$(200/\pi)\ mH$$, a capacitance of $$(10^{-3}/\pi)F$$ and a resistance of $$10\ \Omega$$ are connected in series with an $$a.c$$ source $$220\ v,50\ Hz$$. The phase angle of the circuit is
  • $$\pi/6$$
  • $$\pi/4$$
  • $$\pi/2$$
  • $$\pi/3$$
In a series resonant R-L-C circuit, if L is increased by $$25\%$$ and $$C$$ is decreased by $$20\%$$, then the resonant frequency will :
  • Increases by $$10\%$$
  • Decreases by $$10\%$$
  • Remain unchanged
  • Increases by $$2.5\%$$
Calculate the capacitive reactance of a condenser in order to run a bulb rated at $$10\ watt\ 60\ volt$$ when connected in series to an a.c. source of $$100\ volt$$.
  • $$100\Omega$$
  • $$360\Omega$$
  • $$600\Omega$$
  • $$480\Omega$$
The phase difference between current and voltage in an AC circuit is $$\pi/4$$ radian. If the frequency of AC is $$50 Hz$$, then the phase difference is equivalent to the time difference -  
  • $$0.78s$$
  • $$15.7 ms$$
  • $$0.25s$$
  • $$2.5 ms$$
In a series L-R circuit, connected with a sinusoidal ac source, the maximum potential difference across L and R are respectively 3 volts and 4 volts.
At an instant the potential difference across resistor is 2 volts, across the inductor at the same instant will be:
  • 6
  • 3 cos $$30^{\circ}$$
  • 3 cos $$60^{\circ}$$
  • 6 sec $$45^{\circ}$$
An inductor coil stores U energy when I current is passed through it and dissipates energy at the rate of P. The time constant of the circuit, when this coil is connected across a battery of zero internal resistance is
  • $$\frac{4U}{P}$$
  • $$\frac{U}{P}$$
  • $$\frac{2U}{P}$$
  • $$\frac{2P}{U}$$
The time constant of a circle is $$10 sec$$. When $$10$$ $$\Omega$$ resistance is connected in a series, then constant of a circuit is now $$2$$ sec. Self-inductance of circuit will be
  • $$2.5 H$$
  • $$5 H$$
  • $$15 H$$
  • $$25 H$$
A L-C circuit (inductance 0.01 H, capacity $$1\mu F$$) is connected to a variable frequency ac source. If frequency varies from 1 kHz to 2  kHz, then frequency at which the current in LC circuit is zero is at
  • 1.2 kHz
  • 1.4 kHz
  • 1.6 kHz
  • 1.8 kHz
What is the $$r.m.s.$$ value of an alternating current which when passed through a resistor produces head which is thrice of that produced by a direct current of $$2$$ amperes in the same resistor:-
  • $$6\ amp$$
  • $$2\ amp$$
  • $$3.46\ amp$$
  • $$0.66\ amp$$
Impedence of L-R circuit is
  • $${R}^{2}+{w}^{2}{L}^{2}$$
  • $$\sqrt{R+wL}$$
  • $$R+wL$$
  • $$\sqrt{{R}^{2}+{w}^{2}{L}^{2}}$$
In an $$A.C$$. circuit, a resistance $$R=40\ \Omega$$ and an inductance $$L$$ are connected in series. If the phase angle between voltage and current is $$45^{o}$$, then the value of the  inductive reactance will be
  • $$20\ \Omega$$
  • $$40\ \Omega$$
  • $$10\ \Omega$$
  • $$50\ \Omega$$
A series R LC circuit has a bandwidth of $$300 rad/sec$$ at a resonance frequency of $$3000 rad/ sec $$ when excited by voltage  source of $$100 V$$. The inductance of coil is $$0.1 H$$ the value of R and voltage across C are respectively.
  • $$ 10 \Omega and 1000 V $$
  • $$30 \Omega and 100 V$$
  • $$30 \Omega and 1000 V$$
  • $$300 \Omega and 1000 V$$
In LC parallel circuit L=10 mH and $$C=9\mu F$$. What is the frequency if inductive reactance is equal to capacities reactance?  
  • 5.3 kHz
  • 0.53 kHz
  • 53 kHz
  • 50 kHz
A coil has reactance of $$100\Omega$$ when the frequency is $$50 Hz$$. If the frequency becomes $$150 Hz$$, then the reactance will be
  • $$100\Omega$$
  • $$300\Omega$$
  • $$450\Omega$$
  • $$600\Omega$$
In the following circuit the emf source is $$E_0 = 200 \ volt, \ R = 20 \Omega$$, L = 0.1 henry. C = 10.6 farad and frequency is variable then the current at frequency f = 0 and f = $$\infty$$ is
1284054_d9be57ad7b5e4b96aa702e7e6e72c62a.GIF
  • Zero, 10 A
  • 10 A, zero
  • 10 A, 10 A
  • Zero, zero
In the given circuit,$$\mathrm { V } _ { \mathrm { CE } }$$ =30 V, $$\mathrm { V } _ { \mathrm { BB } }$$ =20 V, $$R _ { B }$$ 1 M $$\Omega$$ ,$$R _ { C }$$ 10 K $$\Omega$$ Neglecting $$v _ { \mathrm { BE } }$$  and taking $$\beta$$ 50, the values of $$\mathbf { I } _ { C }$$  and $$\mathbf { I } _ { \mathrm { E } }$$ are respectively 
1289178_13f2ed40d46a4a45bce420e11430eeac.jpg
  • $$1 \mathrm { mA } , 1.02 \mathrm { mA }$$
  • $$2 \mathrm { mA } , 2.02 \mathrm { mA }$$
  • $$10 \mathrm { mA } , 1 \mathrm { mA }$$
  • $$2 \mathrm { mA } , 0.99 \mathrm { mA }$$
For a series RLC circuit $$R={X}_{L}=2{X}_{C}$$. The impedance of the circuit and phase difference (between) $$V$$ and $$i$$ will be
  • $$\cfrac { \sqrt { 5 } R }{ 2 } ,\tan ^{ -1 }{ \left( 2 \right) } $$
  • $$\cfrac { \sqrt { 5 } R }{ 2 } ,\tan ^{ -1 }{ \left( \cfrac { 1 }{ 2 } \right) } \quad $$
  • $$\sqrt{5}{X}_{C},\tan ^{ -1 }{ \left( 2 \right) } $$
  • $$\sqrt{5}R,\tan ^{ -1 }{ \left( \cfrac { 1 }{ 2 } \right) } $$
A direct current of 10 A is superimposed on an alternating current $$l=40\cos\omega t\left( A \right) $$ flowing through a wire. The effective value of the resulting current will be 
  • $$10\sqrt { 2 } A$$
  • $$20\sqrt { 2 } A$$
  • $$20\sqrt { 3 } A$$
  • 30 A
A student connects a long air cored coil of manganin wire to a $$100VD.C.$$ supply and records a current of $$25amp$$. When the same coil is connected across $$100V.50z a.c.$$ the current reduces to $$20A$$, the reactance of the coil is:-
  • $$4\Omega$$
  • $$3\Omega$$
  • $$5\Omega$$
  • $$None$$
The most appropriate I-H curve for a paramagnetic substance is:
1321308_79fca804ec6746c98765ec69fb950964.PNG
  • $$OA$$
  • $$OB$$
  • $$OC$$
  • $$OD$$
Alternating current is given by i = (3 sin $$\omega$$ t + 4 cos $$\omega$$ t)A  the rms current will be
  • $$\frac{7}{\sqrt 2}$$ A
  • $$\frac{1}{\sqrt 2}$$ A
  • $$\frac{5}{\sqrt 2}$$ A
  • $$\frac{3}{\sqrt 2}$$ A
If the power factor changes from $$\dfrac {1}{2}$$ to $$\dfrac {1}{4}$$ then the increase in impedance in AC circuit with constant resistance is
  • $$20\%$$
  • $$50\%$$
  • $$25\%$$
  • $$100\%$$
In the given circuit $$R$$ is a resistor. $$L$$ is an inductor and $$B _ { 1 }$$ and $$B _ { 2 }$$ are two bulbs and initially the switch $$S$$ was closed. If the switch $$S$$ is turned off. Then 
1330037_0f765b3f65b842a2934359908b9fe605.png
  • Both $$B _ { 1 }$$ and $$B _ { 2 }$$ die out promptly
  • Both $$B _ { 1 }$$ and $$B _ { 2 }$$ die out with some delay
  • $$B _ { 1 }$$ die out promptly but $$B _ { 2 }$$ with some delay
  • $$B _ { 2 }$$ die out promptly but $$B _ { 1 }$$ with some delay
From the figure shown, a series L-C-R circuit connected to a variable frequency $$200\, V$$ source. $$L=5H,\, C=80\, \mu F$$ and $$R=40 \Omega$$. Then the source frequency which drives the circuit at resonance is
1318617_1413a87514524af8bb041489dba6534d.PNG
  • $$25\, Hz$$
  • $$\frac {25}{\pi}\, Hz$$
  • $$50\, Hz$$
  • $$\frac {50}{\pi}\, Hz$$
An inductor ($$X_L=2 \Omega$$) a capacitor ($$X_c=8 \Omega$$) and a resistance $$(8 \Omega)$$ are connected in series with an ac source. The voltage output of A.C source is given by v=10 cos 100 $$\pi t$$. The instantaneous p.s. between A and B, when it is half of the voltage output from source at that instant will be:
1302362_938c7e7801eb4fc397e9ab0b2271abca.png
  • $$\dfrac{24}{7} volts$$
  • $$\dfrac{24}{5} volts$$
  • $$\dfrac{7}{24} volts$$
  • $$\dfrac{5}{24} volts$$
A $$50Hz$$ alternating current of peak value $$1$$ ampere flows through the primary coil of a transformer. If the mutual inductance between the primary and secondary be $$1.5$$ henry, then the mean value of the induced voltage is:
  • $$75$$ volt
  • $$150$$ volt
  • $$225$$ volt
  • $$300$$ volt
In a series LCR circuit K = 200 S2 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 byOn taking out the indicator from the circuit the current leads the voltage byThe power dissipated in the LCR circuit is :

  • 342 W
  • 305 K
  • 209 K
  • 242 K
In the circuit shown in figure. the a.c. source gives a voltage V = 20 $$\cos ( 200 \pi + 1 )$$ The reading of vulimeter and amineter will be
1339394_d8f5e3ad5d904c2a8d819d4d7201b5da.png
  • $$0 \mathrm { V } , 0.47 \mathrm { A }$$
  • $$5.6 \mathrm { V } , 1.4 \mathrm { A }$$
  • $$0 \mathrm { V } , 1.4 \mathrm { A }$$
  • $$\frac { 2 \mathrm { R } } { ( 2 \mu - 1 ) }$$
The power factor of a circuit in which a box having unknown electrical devices connected in series with a resistor of resistance $$3\Omega$$ is $$3/5$$. The reactance  of the box is
  • $$5\Omega$$
  • $$\dfrac{5}{3\omega }$$
  • $$4\Omega$$
  • $$\dfrac{4}{3\omega }$$
The time taken by an ac of 50 Hz in reaching from zero to its rms value is 
  • 20 ms
  • 10 ms
  • 5 ms
  • 2.5 ms
If resonant frequency of a R-L-C circuit is $$\Delta \omega $$, then which of the following quantity is regarded as a measure of the sharpness of resonance?
  • $$\frac { \omega _0 }{ \Delta\omega } $$
  • $$\frac { \omega _0 }{ 2\Delta\omega } $$
  • $$\frac { 2\omega _0 }{ \Delta\omega } $$
  • $$\frac { \omega _0 }{ 2\omega } $$
The phase difference between the alternating current and emf is $$\pi /2$$. Which of the following cannot be the constituent of the circuit?
  • $$R$$ alone
  • $$RL$$
  • $$LC$$
  • $$L$$ alone
An alternating current is given by
$$i={i}_{1}\cos{\omega t}+{i}_{2}\sin{\omega t}$$. The rms current is given by:
  • $$\cfrac{{i}_{1}+{i}_{2}}{\sqrt{2}}$$
  • $$\cfrac { \left| { i }_{ 1 }+{ i }_{ 2 } \right| }{ \sqrt { 2 } } $$
  • $$\sqrt { \cfrac { { i }_{ 1 }^{ 2 }+{ i }_{ 2 }^{ 2 } }{ 2 } } $$
  • $$\sqrt { \cfrac { { i }_{ 1 }^{ }+{ i }_{ 2 }^{ } }{ 2 } } $$
The tuned collector oscillator circuit used in the local oscillator of a radius receiver makes use of a tuned circuit with $$L=60\mu H$$ and $$C=400pF$$.
Calculate the frequency of oscillations
  • $$1.03KHz$$
  • $$1.03Hz$$
  • $$1.03GHz$$
  • $$1.03MHz$$
Current through an AC series circuit is 4 A if operated at resonant frequency $${\omega _o}/2.$$ current reduces to 2 . A then at $$2{\omega _o}.$$ current in the :  
  • $$\sqrt 2 A$$
  • $$1\,A$$
  • $$2\,A$$
  • $$3\,A$$
Growth of current in two different L-R circuit are depicted by the I-t graphs shown. Angle subtended by the curves with time axis at time t=0 are also shown in the graph $${ \tau  }_{ 1 }$$ and $${ \tau  }_{ 2 }$$ are time constants for the circuits 1 and 2 respectively. Choose the CORRECT alternative
1347954_fb421deae51c406f82ce2f2f4551d094.png
  • $$\frac { { \tau }_{ 1 } }{ { \tau }_{ 2 } } =\frac { 2 }{ 3 } $$
  • $$\frac { { \tau }_{ 1 } }{ { \tau }_{ 2 } } =\frac { 3 }{ 2 } $$
  • Initial rate of change of current for circuit-2 is 2 times that of circuit-1
  • Initial rate of change of current for circuit-2 is 4 times that of circuit-1
In an AC circuit instantaneous current is given by $$i=i_0sin\dfrac{\pi}{6}t.$$ The time from starting when current in circuit becomes equal to its rms value for the first time is 
  • $$1.5s$$
  • $$2s$$
  • $$2.5s$$
  • $$3s$$
A potential difference of $$6V$$ is applied to a coil of inductance $$0.5\ H$$ and a resistance of $$4\ ohm$$ connected in series. The time taken for the current to reach half is maximum value is (in seconds).
  • $$\dfrac {\log_{e}{2}}{8}$$
  • $$\dfrac {\log_{e}{2}}{4}$$
  • $$\dfrac {\log_{e}{4}}{8}$$
  • $$\dfrac {\log_{e}{8}}{4}$$
In a series resonant LCR circuit, the voltage across $$ R  $$ is 100$$  V  $$ and $$  R= $$ 1$$  k \Omega  $$ with $$  C $$ $$ =2 \mu F . \operatorname{The} $$ resonant frequency $$  \omega  $$ is 200 $$ \mathrm{rad} / \mathrm{s}  $$ . At resonance the voltage across L is:
  • $$ 25 \times 10^{-2} V $$
  • $$40$$ $$ V $$
  • $$250$$ $$ \mathrm{V} $$
  • $$ 4 \times 10^{-3} \mathrm{V} $$
The effective resistance between A and B in the given circuit is 
1388937_d7d6c76e127a4da59741eff8ed4bda67.PNG
  • $$ 2 \Omega $$
  • $$ 7 \Omega $$
  • $$ 3 \Omega $$
  • $$ 6 \Omega $$
The current (i) in the inductance is varying with according to the plot shown in figure.
Which one of the following is the correct variation of voltage with time in the coil?
1402221_33c616c57c6345f181fe367c5cd2df77.png
A coil of induction $$0.5\ H$$ is connected to a $$18\ V$$ battery. The rate of growth of current in the inductor, just after the switch $$'S'$$ is closed.
1402025_d61d0b50d4cb46eba97b3f161b58be59.png
  • $$Zero$$
  • $$18\ A/s$$
  • $$36\ A/s$$
  • $$Infinite$$
Which of the following combinations should be selected for better tunning of an $$LCR$$ circuit used for communication
  • $$ R=20 \Omega, L= $$ $$ =1.5 H, C=35 \mu $$
  • $$ R=25 \Omega $$ $$ L=2.5 H $$,$$ C=45 \mu F $$
  • $$ R=15 \Omega, L=3.5 H, C=30 \mu F $$
  • $$ R=25 \Omega, L $$ $$ =1.5 H, C= $$ $$45$$ $$ \mu F $$
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