CBSE Questions for Class 12 Medical Physics Alternating Current Quiz 1 - MCQExams.com

Which one of the following represents capacitive reatance versus angular frequency graph?
The frequency at which $$1\ H$$ inductor will have a reactance of $$2500\ \Omega$$ is:
  • $$418\ Hz$$
  • $$378\ Hz$$
  • $$398\ Hz$$
  • $$406\ Hz$$
A series AC circuit has a resistance of $$4\Omega $$ and a reactance of $$3\Omega$$. The impedance of the circuit is 
  • $$5\,\Omega$$
  • $$7\,\Omega$$
  • $$12/7\,\Omega$$
  • $$7/12\,\Omega$$
The ratio of peak value and r.m.s value of an alternating current is
  • $$ 1 $$
  • $$ \dfrac{1}{2} $$
  • $$ \sqrt{2} $$
  • $$ \dfrac{1}{\sqrt{2}} $$
In a circuit $$LC = 10^{-3}H, C = 10^{-3} F$$. Find angular frequency.
  • $$1000 \,rad/sec$$
  • $$100 \,rad/sec$$
  • $$10 \,rad/sec$$
  • $$10^{-3} \,rad/sec$$
Alternating current is flowing in inductance $$L$$ and resistance $$R$$. The frequency of source is $$\omega/2\pi$$ Which of the following statement in correct:
  • For low frequency the limiting value of impedance is $$L$$.
  • For high frequency the limiting value of impedance is $$\omega L$$.
  • For high frequency the limiting value of impedance is $$R$$.
  • For low frequency the limiting value of impedance is $$\omega L$$.
The power factor of L-R circuit is :
  • $$\dfrac{R}{\omega L}$$
  • $$\dfrac{R}{(\omega L)^2+R^2}$$
  • $$\omega LR$$
  • $$\sqrt{\omega LR}$$
Current in the circuit is wattless, if
  • Inductance in the circuit is zero
  • Resistance in the circuit is zero
  • Current is alternating
  • Resistance and inductance both are zero
An inductance of $$2H$$ , capacitance of $$8\mu F$$ and resistance of  $$10K\Omega$$ are connected in series to an AC source of $$100V$$ with adjustable frequency. The angular frequency at which current in the circuit is maximum is :
  • $$50 \ rad/s$$
  • $$100 \ rad/s$$
  • $$125 \pi \ rad/s$$
  • $$250 \ rad/s$$
If $${W_1}and\;{W_2}$$ are half power frequencies of series LCR circuit, Then the reasonant frequency of the circuit is-
  • $$\sqrt {{W_1}\;{W_2}} $$
  • $$\frac{{{W_1} + {W_2}}}{2}$$
  • $$\sqrt {\frac{{{W_1} + {W_2}}}{2}} $$
  • $$\frac{{{W_1} -{W_2}}}{2}$$
In an a.c. circuit consisting of resistance $$R$$ and inductance $$L$$, the voltage across $$R$$ is $$60$$ volt and that across $$L $$ is $$80$$ Volt.The total Voltage across the combination is 
  • $$140 V$$
  • $$20 V$$
  • $$100 V$$
  • $$70 V$$
In a series LCR circuit, the voltage across R is 100 volts and R = 1 $$k\Omega$$ with C = $$2\mu F$$. The resonant frequency $$\omega$$ is 200 rad/s. At resonance the voltage across L is-
  • $$2.5 \times 10^{-2}V$$
  • $$40 V$$
  • $$250 V$$
  • $$4 \times 10^{-3}V$$
The instantaneous value of emf and current in an A.C. circuit are; $$E=1.414sin\left ( 100\pi t-\frac{\pi }{4} \right )$$ , $$I=0.707sin(100\pi t)$$ . The admittance of the circuit will be _______ mho.
  • $$\dfrac{1}{\sqrt{2}}$$
  • $$\sqrt{2}$$
  • $$\dfrac{1}{2}$$
  • $$2$$
The instantaneous value of emf and current in an A.C. circuit are $$E=1.414$$sin( $$100\pi t-\frac{\pi }{4} $$) , $$ I=0.707$$ sin($$100\pi t$$) . The resistance of the circuit is
  • $$2\Omega $$
  • $$\sqrt{2}\Omega $$
  • $$\frac{1}{\sqrt{2}}\Omega$$
  • $$\frac{1}{2}\Omega$$
$$A$$ series $$R-C$$ circuit is connected to $$AC$$ voltage source. $$C$$onsider two cases; ($$A$$) when $$C$$ is without a dielectric medium and (B) when $$C$$ is filled with dielectric of constant $$4$$. The current $$I_{R}$$ through the resistor and voltage $$V_{C}$$ across the capacitor are compared in the two cases. Which of the following $$is/are$$ true?
  • $$I_{R}^{A}>I_{R}^{B}$$
  • $$I_{R}^{A} < I_{R}^{B}$$
  • $$V_{c}^{A}>V_{c}^{B}$$
  • $$V_{C}^{A} < V_{R}^{C}$$
The instantaneous value of emf and current in an A.C. circuit are; $$E=1.414sin\left ( 100\pi t-\frac{\pi }{4} \right )$$ , $$I=0.707sin(100\pi t)$$ . The impedance of the circuit will be
  • $$1\Omega $$
  • $$2\Omega $$
  • $$\sqrt{2}\Omega $$
  • $$\dfrac{1}{2}\Omega $$
The capacitive reactance of 50 $$\mu$$F capacitance at a frequency of $$2 \times 10^{3}$$Hz will be ____ $$\Omega $$
  • $$\frac{2}{\pi }$$
  • $$\frac{3}{\pi }$$
  • $$\frac{4}{\pi }$$
  • $$\frac{5}{\pi }$$
The phase angle between current and voltage in a purely inductive circuit is :
  • $$zero$$
  • $$\pi $$
  • $$\pi $$/4
  • $$\pi $$/2
In an LCR 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
When the rms voltages $$V_L, V_C$$ and $$V_R$$ are measured respectively across the inductor L, the capacitor C and the resistor R in a series LCR circuit connected to an AC source, it is found that the ratio $$V_L : V_C : V_R=1 : 2 : 3$$. If the rms voltage of the AC source is 100 V, then $$V_R$$ is close to :
  • 50 V
  • 70 V
  • 90 V
  • 100 V
In a series resonant $$LCR$$ circuit, the voltage across $$R$$ is $$100\ volts$$ and $$R = 1k\ \Omega $$ with $$C=2\ \mu F$$. The resonant frequency is $$200\ rad/s$$. At resonance the voltage across $$L$$ is 
  • $$4$$ x $$10^{-3}\ V$$
  • $$2.5$$ x $$10^{-2}\ V$$
  • $$40\ V$$
  • $$250\ V$$
In an LCR circuit as shown below both switches are open initially. Now switch $$S_{1}$$ is closed, $$S_{2}$$ kept open. ( $$q$$ is charge on the capacitor and $$\tau=RC$$ is capacitive time constant). Which of the following statement is correct?

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  • At $$ t=\tau,\ q=CV/2$$
  • At $$ t=2\tau,\ q=CV(1-e^{-2})$$
  • At $$ t=\frac{T}{2},\ q=CV(1-e^{-1})$$
  • Work done by the battery is half of the energy dissipated in the resistor.
In a series LCR circuit $$\mathrm{R}=200\ Omega$$ and the voltage and the frequency of the main supply is $$220$$ $$V$$ and $$50$$ $$Hz$$ respectively. On taking out the capacitance from the circuit the current lags behind the voltage by $$30^0$$. On taking out the inductor from the circuit the current leads the voltage by $$30^0$$. The power dissipated in the LCR circuit is
  • $$305$$ $$\mathrm{W}$$
  • $$210$$ $$\mathrm{W}$$
  • $$Zero \mathrm{W}$$
  • $$242$$ $$\mathrm{W}$$
An arc lamp requires a direct current of 10A at 80V to function. If it  is connected to a 220V (rms), 50 Hz AC supply, the series inductor needed  for it to work is close to:
  • 80H
  • 0.08H
  • 0.044H
  • 0.065H
In an a.c. circuit, the instantaneous e.m.f. and current are given by $$e=100 \sin 30t$$, $$i=20\sin\left(30t -\displaystyle\frac{\pi}{4}\right)$$. In one cycle of a.c., the average power consumed by the circuit and the wattles current are, respectively.
  • $$\displaystyle\frac{50}{\sqrt{2}}, 0$$
  • $$50, 0$$
  • $$50, 10$$
  • $$\displaystyle\frac{1000}{\sqrt{2}}, 10$$
In an LCR series a.c. circuit, the voltage across each of the components. L, C and R is 50 V. The voltage across the LC combination will be; 
  • $$50\ \text{V}$$
  • $$50\sqrt{2}\mathrm{v}$$
  • $$100\ \text{V}$$
  • $$0\mathrm{V}$$ (zero)
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) :

28922_ed61fd47e47a4f50804417ea346ab468.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.
In the circuit shown, $$L = 1 \mu H, C = 1 \mu F$$ and $$R = 1 k\Omega$$. They are connected in series with an a.c. source $$V = V_0 \sin \omega t$$ as shown. Which of the following options is/are correct? 

640514_d7d8d01883fa4b5ba57ce8a591632f7f.png
  • At $$\omega >> 10^6 rad. s^{-1}$$, the circuit behaves like a capacitor
  • At $$\omega \sim 0$$ the current flowing through the circuit becomes nearly zero
  • The current will be in phase with the voltage if $$\omega = 10^4rad. s^{-1}$$
  • The frequency at which the current will be in phase with the voltage is independent of $$R $$
A series LR circuit is connected to a voltage source with $$V\left( t \right) ={ V }_{ 0 }\sin { \Omega t } $$. After very large time, current $$I\left( t \right) $$ behaves as $$\left( { t }_{ 0 }\gg \frac { L }{ R }  \right) $$
$$A$$ series $$R-C$$ combination is connected to an $$AC$$ voltage of angular frequency $$(\omega =500radian/s$$. lf the impedance of the $$R-C$$ circuit is $$R\sqrt{1.25}$$, the time constant (in millisecond) of the circuit is
  • 1
  • 2
  • 3
  • 4
A $$40 \mu F$$ capacitor is connected to a $$200 V,\ 50 Hz \ ac$$ supply. The rms value of the current
in the circuit is, nearly :
  • $$2.05 A$$
  • $$2.5 A$$
  • $$25.1 A$$
  • $$1.7 A$$
A series R-C circuit is connected to an alternating voltage source. Consider two situation:
(a) When capacitor is filled
(b) When capacitor is mica filled
Current through resister is i and voltage across capacitor is V then :
  • $$V_a=V_b$$
  • $$V_a < V_b$$
  • $$V_a>V_b$$
  • $$i_a = i_b$$
An inductor $$20$$ mH, a capacitor $$100$$ $$\mu$$F and a resistor $$50$$ $$\Omega$$ are connected in series across a source of emf, V$$=10$$ $$\sin 314$$t. The power loss in the circuit is?
  • $$2.74$$ W
  • $$0.79$$ W
  • $$1.13$$ W
  • $$0.43$$ W
  • Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
  • Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
  • Assertion is correct but Reason is incorrect
  • Both Assertion and Reason are incorrect
A condenser of $$250\mu F$$ is connected in parallel to a cell of inductance $$0.16$$ mH, while its effective resistance is while its. Determine the resonant frequency.
  • $$9\times 10^4$$Hz
  • $$16\times 10^7$$ Hz
  • $$8\times 10^5$$ Hz
  • $$9\times 10^3$$ Hz
Reciprocal of Impedance is:
  • Susceptance
  • Conductance
  • Admittance
  • Transconductance
A $$10\ \mu F$$ capacitor is connected across a $$200\  V$$, $$ 50 \ Hz$$ A.C. supply. The peak current through the circuit is :
  • $$0.6\  A$$
  • $$0.6\sqrt{2}A$$
  • $$(0.06\sqrt{2})A$$
  • $$0.6{\pi}\ A$$
If resonant frequency is $$f$$ and capacitance become $$4$$ times, then resonant frequency will be :
  • $$\dfrac {f}{2}$$
  • $$2f$$
  • $$f$$
  • $$\dfrac {f}{4}$$
In a circuit, the frequency is $$f=\dfrac{1000}{2\pi }$$Hz and the inductance is 2 henry, then the reactance will be
  • 200$$\Omega $$
  • 200$$ \mu$$ $$\Omega $$
  • 2000$$\Omega $$
  • 2000$$ \mu$$ $$\Omega $$
The instantaneous value of emf and current in an A.C. circuit are: $$E=1.414sin\left ( 100\pi t-\frac{\pi }{4} \right )$$, $$I=0.707sin(100\pi t)$$ .The reactance of the circuit
will be
  • $$\sqrt{2}$$ $$\frac{1}{2}\Omega$$
  • 2$$\Omega$$
  • $$\frac{1}{2}\Omega$$
  • $$\frac{1}{\sqrt{2}}\Omega$$
The instantaneous value of emf and current in an
A.C. circuit are; $$E=1.414sin\left ( 100\pi t-\dfrac{\pi }{4} \right )$$ ,
$$I=0.707sin(100\pi t)$$ . RMS value of current will be
  • 1A
  • $$\dfrac{1}{\sqrt{2}}A$$
  • $$\sqrt{2}A$$
  • $$\dfrac{1}{2}A$$
The instantaneous value of emf and current in an A.C. circuit are; $$E=1.414sin\left ( 100\pi t-\dfrac{\pi }{4} \right )$$ , $$I=0.707sin(100\pi t)$$. The RMS value of emf will be
  • $$2\sqrt{2}V$$
  • $$1 V$$
  • $$\dfrac{1}{2}V$$
  • $$\dfrac{1}{2\sqrt{2}}V$$
In an AC circuit containing only capacitance, the current :
  • leads the voltage by 180
  • lags the voltage by 90
  • leads the voltage by 90
  • remains in phase with the voltage
An inductive coil has a resistance of 100 $$\Omega $$ . When an AC signal of frequency 1000 Hz is applied to the coil, the voltage leads the current by $$45^{o}$$. The inductance of the coil is
  • $$\dfrac{1}{100\pi }$$H

  • $$\dfrac{1}{20\pi }$$H
  • $$\dfrac{1}{40\pi }$$H
  • $$\dfrac{1}{60\pi }$$H
If the phase difference between Alternating Voltage and Alternating Current is $$\frac{\pi }{6}$$ and the resistance in the circuit is $$\sqrt{300}\Omega $$ , then the impedance of the circuit will be
  • 25$$\Omega $$
  • 50$$\Omega $$
  • 20$$\Omega $$
  • 100$$\Omega $$
The inductance of a resistanceless coil is 0.5 henry. In the coil, the value of alternating current is 0.2 A, whose frequency is 50 Hz. The reactance of circuit is
  • 15.7$$\Omega $$
  • 157$$\Omega $$
  • 1.57$$\Omega $$
  • 757$$\Omega $$
The capacitive reactance at 1600Hz is 81 $$\Omega $$ .When the frequency is doubled then the capacitive reactance will be:
  • 40.5$$\Omega $$
  • 81$$\Omega $$
  • 162$$\Omega $$
  • zero
In an LCR circuit, current is I $$=$$ 10sin100$$\pi$$ t from an A.C. source. The value of average voltage at the ends of the resistance R $$=$$ 10$$\Omega $$ will be
  • 25V
  • $$\dfrac{25}{\sqrt{2}}V$$
  • zero V
  • 1V
In an A.C. circuit the potential difference across an inductance and resistance joined in series are respectively 16V and 20V. The total potential difference across the circuit is
  • 20.0V
  • 25.6V
  • 31.9V
  • 53.5V
A coil is used in a circuit in which an A.C. of frequency 50Hz is flowing. The self-inductance of the coil, in order to produce an impedance of 100 $$\Omega $$ , will be ___ H
  • $$ \pi$$
  • $$\frac{1}{\pi }$$
  • $$ \pi ^{2}$$
  • $$\frac{1}{\pi^{2} }$$
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