CBSE Questions for Class 12 Medical Physics Alternating Current Quiz 13 - MCQExams.com

The value of resistance of the coil calculated by the student is :
  • $$3\Omega$$
  • $$4\Omega$$
  • $$5\Omega$$
  • $$8\Omega$$
In the circuit shown in figure,

224066.JPG
  • $$V_R=80V$$
  • $$X_C=50\Omega$$
  • $$V_L=40V$$
  • $$V_0=100V$$
A resistor and a capacitor are connected to an A.C. supply of $$200\space V, \space 50\space Hz$$ in series. The current in the circuit is $$2\space A$$. If the power consumed in the circuit is $$100\space W$$ then the capacitive reactance in the circuit is
  • $$100\space \Omega$$
  • $$25\space \Omega$$
  • $$\sqrt{125\times75}\space \Omega$$
  • $$400\space \Omega$$
A $$50\ Hz$$ a.c. source of $$20\ V$$ is connected across R and C as shown in figure below. The voltage across R is $$12\ V$$. The voltage across C is:
294113.png
  • $$8\ V$$
  • $$16\ V$$
  • $$10\ V$$
  • not possible to determine unless values of R and C are given
A series $$LCR$$ circuit containing a resistance of $$120\space \Omega$$ has angular resonance frequency $$4\times10^5\space rad\space s^{-1}$$. At resonance the voltages across resistance and inductance are $$60\space V$$ and $$40\space V$$, respectively. The value of inductance $$L$$ is
  • $$0.1\space mH$$
  • $$0.2\space mH$$
  • $$0.35\space mH$$
  • $$0.4\space mH$$
The inductance of the coil is
  • $$0.02\space H$$
  • $$0.04\space H$$
  • $$0.08\space H$$
  • $$1.0\space H$$
The impedance of $$P$$ at this frequency is :
224442_2a9f790dda0f4e4387f6380bff2529c0.jpg
  • $$77\space \Omega$$
  • $$36\space \Omega$$
  • $$40\space \Omega$$
  • $$125\space \Omega$$
When $$100\space V$$ dc is applied across a coil, a current of $$1\space A$$ flows through it and when $$100\space V$$ ac of $$50\space Hz$$ is applied to the same coil, only $$0.5\space A$$ flows. The inductance of coil is
  • $$5.5\space H$$
  • $$3/\pi\space H$$
  • $$\sqrt3/\pi\space H$$
  • $$2.5\space H$$
The impedance of $$Q$$ at this frequency is:
224445_6bcdf665c0c24f00ba21a4fa04b7409a.jpg
  • $$200\space \Omega$$
  • $$\sqrt{1350}\space \Omega$$
  • $$55\space \Omega$$
  • $$\sqrt{9524}\space \Omega$$
In the circuit shown in the figure, the A.C. source gives a voltage V = 20 cos (2000 t) volt. Neglecting source resistance, select correct alternative(s).
294755.png
  • The reading of voltmeter is 0 V
  • The reading of voltmeter is 5.6 V
  • The reading of ammeter is 1.4 A
  • The reading of ammeter is 0.47 A
In a purely inductive circuit, the current is
  • In phase with the voltage
  • Out of phase with the voltage
  • Leads the voltage by $$\pi/ 2$$
  • Lags behind the voltage $$\pi/ 2$$
If the power factor in a circuit is unit, then the impedance of the circuit is
  • Inductive
  • Capacitive
  • Partially inductive and partially capacitive
  • Resistive
An oscillating circuit of a capacitor with capacitance $$C$$, a coil of inductance $$L$$ with negligible resistance, and switch. With the switch disconnected the capacitor was charged to a voltage $$V_m$$ and then at the moment $$t=0$$, the switch was closed. The current $$I$$ in the circuit as a function of time is represented as 
  • $$V_m\sqrt{\frac{L}{C}} sin (wt)$$
  • $$V_m\sqrt{\frac{C}{L}} sin (wt)$$
  • $$V_m\sqrt{\frac{L}{C}} cos (wt)$$
  • $$V_m\sqrt{\frac{C}{L}} sin (wt)$$
A square conducting loop of side L is situated in gravity free space. A small conducting circular loop of radius r ( r < < L) is placed at the center of the  square loop, with its plane perpendicular to the plane of the square loop. The mutual inductance of the two coils is
  • $$\dfrac{2\sqrt2 \mu_sI}{L}r^2$$
  • $$\dfrac{\sqrt2 \mu_sI}{L}r^2$$
  • 0
  • None of these
In a LR circuit of $$3\;mH$$ inductane and $$4\;\Omega$$ resistance, emf $$E=4\;cos\;(1000\;t)$$ volt is applied. The amplitude of current is:
  • $$0.8\ {A}$$
  • $$\dfrac{4}{7}\ {A}$$
  • $$1.0\ {A}$$
  • $$\dfrac{4}{\sqrt{7}}\ {A}$$
A series LCR circuit is connected across a source of alternating emf of changing frequency and resonates at frequency $$\text{f}_o$$. Keeping capacitance constant, if the inductance (L) is increased by $$\sqrt{3}$$ times and resistance(R) is increased  by 1.4 times, the resonant frequency now is:
  • $$3^{1/4}\text{f}_0$$
  • $$\sqrt{3}\text{f}_0$$
  • $$(\sqrt{3}-1)^{1/4}\text{f}_0$$
  • $$\left(\dfrac{1}{3}\right)^{1/4}\text{f}_0$$
The given graph shows variation with time in the source voltage and steady state current drawn by a series RLC circuit.
Which of the following statements is/are correct?

294836.png
  • Current lags the voltage
  • Resistance in the circuit is 250 $$ \sqrt {3} \Omega $$
  • Reactance in the circuit is 250 $$ \Omega $$
  • Average power dissipation in the circuit is 20 $$ \sqrt {3} $$ W
A charged capacitor discharges through a resistance R with time constant $$ \tau $$. The two are now placed in series across an AC source of angular frequency $$\displaystyle \omega = \frac {1} {\tau} $$ . The impedance of the circuit will be:
  • $$\displaystyle \frac {R} {\sqrt {2}} $$
  • R
  • $$ \sqrt {2} $$ R
  • 2R
An AC generator producing $$10V$$ (rms) at $$200rad/s$$ is connected in series with a $$50\Omega $$ resistor, a $$400mH$$ inductor and a $$200\mu F$$ capacitor. The rms voltage across the inductor is 
  • $$2.5V$$
  • $$3.4V$$
  • $$6.7V$$
  • $$10.8V$$
A $$200$$km long telegraph wire has a capacitance of $$0.014$$ $$\mu F/km$$. If it carries an alternating current of $$50\times 10^3$$Hz, what should be the value of an inductance required to be connected in series so that impedance is minimum?
  • $$0.48\times 10^{-2}$$mH
  • $$0.36\times 10^{-2}$$mH
  • $$0.52\times 10^{-2}$$mH
  • $$0.49\times 10^{-2}$$mH
An inductor and a resistor are connected to an ac supply of $$50 V$$ and $$50 Hz$$. If the voltage across the resistor is $$40 V$$ the voltage across the inductor will be:
  • $$10\ V$$
  • $$20\ V$$
  • $$30\ V$$
  • $$60\ V$$
In an L-R circuit, the voltage is given by $$V$$ as $$283 sin 314t$$. The current is found tc be $$4 \, sin \left ( 314t-\dfrac {\pi}{4} \right )$$Calculate the resistance of the circuit. 
  • $$90\Omega$$
  • $$25 \Omega$$
  • $$50\Omega$$
  • $$75\Omega$$
A RC series circuit of R$$=15\Omega$$ and $$C=10\mu F$$ is connected to $$20$$ volt DC supply for very long time. Then capacitor is disconnected from circuit and connected to inductor of $$10$$mH. Find amplitude of current.
  • $$0.2\sqrt{10}$$A
  • $$2\sqrt{10}$$A
  • $$0.2$$A
  • $$\sqrt{10}$$A
An a.c. source of angular frequency w is fed across a resistor R and a capacitor C in series. It registers a certain current. The frequency of the source decreases by two-third of the original value, maintaining the same voltage, the current in the circuit is found to be halved. Find the ratio of reactance to resistance at the original frequency
  • $$\sqrt{\frac{3}{5}}$$
  • $$\sqrt{\frac{5}{3}}$$
  • $$\sqrt{\frac{2}{3}}$$
  • $$\sqrt{\frac{3}{2}}$$
An L-C-R series circuit containing a resistance of $$R = 120 \Omega $$ has angular resonant frequency $$4 \times 10^5$$ rad/s. At resonance the voltage across resistance and inductance are 60 V and 90 V respectively. Then values of L and C are :
  • $$0.2 \, mH, \dfrac{1}{16}\mu F$$
  • $$0.2 \, mH, \dfrac{1}{32}\mu F$$
  • $$0.4 \, mH, \dfrac{1}{32}\mu F$$
  • $$0.4 \, mH, \dfrac{1}{16}\mu F$$
In the circuit diagram shown, $$X_C=100 \Omega,X_L=200 \Omega\, and \, R=100 \Omega$$. Effective current through the source is :
787970_611702a1d5b24f968e89fa426bb2eb48.png
  • $$2A$$
  • $$2\sqrt{2}A$$
  • $$0.5 A$$
  • $$\sqrt {0.4} A$$
The equivalent inductance between $$A$$ and $$B$$ is:
949843_30f7a256f2994f25be948b41401918cc.png
  • $$1 H$$
  • $$4 H$$
  • $$0.8 H$$
  • $$16 H$$
Two parallel wires in the plane of the paper are distance $$X_0$$ apart. A point charge is moving with speed u between the wires in the same plane at a distance $$X_1$$ from one of the wires. When the  wires carry current of magnitude I in the same direction, the radius of curvature of the path of the point charge is $$R_1$$. In contract, if the currents I in the two wires have directions opposite to each other, the radius of curvature of the path is $$R_2$$. If $$\dfrac{X_0}{X_1}=3$$, the value of $$\dfrac{R_1}{R_2}$$ is?
  • 6
  • $$3$$.
  • 4
  • 5
An alternating voltage given as $$V=100\sqrt { 2 } \sin { 100t } \quad $$is applied to a capacitor of $$1\mu F$$. The current reading of the ammeter will be equal to ______ mA.
  • $$10$$
  • $$20$$
  • $$40$$
  • $$80$$
In an oscillating $$LC$$ circuit the maximum charge on the capacitor is $$Q$$. The charge on the capacitor when the energy is stored equally between the electric and magnetic field is 
  • $$Q/2$$
  • $$Q/\surd 3$$
  • $$Q/\surd 2$$
  • $$Q$$
An electrical device draws $$2 kW$$ power from ac mains voltage $$223 V(rms).$$ The current differs lags in phase by $$\phi = tan^{-1} \left ( -\dfrac{3}{4} \right )$$ as compared to voltage. The resistance R in the circuit is:
  • $$15\Omega$$
  • $$20 \Omega$$
  • $$25 \Omega$$
  • $$30 \Omega$$
A coil of inductance $$300\ mH$$ and resistance $$2\Omega$$ is connected to a source of voltage $$2V$$. The current reaches half of its steady state value in
  • $$0.05\ s$$
  • $$0.1\ s$$
  • $$0.15\ s$$
  • $$0.3\ s$$
For the circuit shown in Fig. the voltage of the source at any instant is equal to 
1050133_d3faae9efe5f47188f2f6cad41a6d7b2.png
  • The sum of the maximum voltages across the elements.
  • The voltage drop across the resistor.
  • The sum of the instantaneous voltages across the elements.
  • The sum of the rms voltages across the elements.
A $$100\ volt$$ $$AC$$ source of angular frequancy $$500\ rad/s$$ is connected to a $$LCR$$ circuit with $$L=0.8\ H$$, $$C=5\ \mu F$$ and $$R=10\Omega$$, all connected in series. The potential difference across the resistance is 
  • $$\dfrac {100}{\sqrt {2}}volt$$
  • $$100\ volt$$
  • $$50\ volt$$
  • $$50\sqrt {3} $$
When $$100\ V\ d.c.$$ flows in a solenoid, the steady state current is $$10\ A$$. When $$100-V.\ ac$$. flows, the current drops to $$0.5\ A$$. If the frequency of ac. be $$50\ Hz$$, then the impedance and the inductance of the solenoid are.
  • $$200\Omega, 0.64\ H$$
  • $$100\Omega, 0.86\ H$$
  • $$200\Omega, 1.0\ H$$
  • $$100\Omega, 0.93\ H$$
A $$0.21 - H $$ inductor and a $$88- \Omega $$ resistor are connected in series to a $$220-V , 50-Hz $$ AC source. The current in the circuit and the phase angle between the current and the source voltage are respectively. Use $$ \pi = 22/7 $$
  • $$ 2 A, tan^{-1} 3/4 $$
  • $$ 14.4 A, tan^{-1} 7/8 $$
  • $$ 14.4 A, tan^{-1} 8/7 $$
  • $$ 3.28 A, tan^{-1} 2/11 $$

In a series  L-C-R circuit the voltage across the resistance , capacitance and inductance is 10 V each. If capacitance is short circuited, the voltage across the inductance will be:
  • $$10\,V$$
  • $$10\sqrt {3}V$$
  • $$10/\sqrt {2}V$$
  • $$20\,V$$
In the circuit shown in figure when the frequency of oscillator in increase, the reading of ammeter $${A}_{4}$$ is same as that of ammeter:
1024254_7faca545d2db441bb057c002d5590a02.png
  • $${A}_{1}$$
  • $${A}_{2}$$
  • $${A}_{3}$$
  • $${A}_{1}$$ and $${A}_{2}$$
An inductor of reactance $$X_L=4\Omega$$ and resistor of resistance $$R=3\Omega$$ are connected in series with a voltage source of emf $$\varepsilon =(20V)[\sin (100\pi rad/s)t]$$. The current in the circuit at any time t will be?
  • $$I=(4A)[\sin (100\pi rad/s)t+37^o]$$
  • $$I=(4A)[\sin (100\pi rad/s)t-37^o]$$
  • $$I=(4A)[\sin (100\pi rad/s)t+53^o]$$
  • $$I=(4A)[\sin (100\pi rad/s)t-53^o]$$
In $$LCR$$ oscillation circuit resistance is $$10\Omega$$ and inductive reactance at resonace condition is $$1\ k\Omega$$. After how many oscillation peak value os current will fall to $$(\dfrac {1}{e})$$ times maximum value of peak current.
  • $$\dfrac {50}{\pi}$$
  • $$100$$
  • $$50$$
  • $$\dfrac {100}{\pi}$$
A coil of $$L=5x10^{-3}H$$ and $$R=18\ \Omega $$ is abruptly supplied a potential of $$5$$ volts .What will be the rate of change of current in $$0.001$$ second? $$(e^{-3.6}-0.0273)$$
  • $$27.3\ amp/sec$$
  • $$27.8\ amp/sec$$
  • $$2.73\ amp/sec$$
  • $$2.78\ amp/sec$$
In the given circuit find the ratio of $$i_{1}$$ to $$i_{2}$$. Where $$i_{1}$$ is the initial (at $$t = 0)$$ current, and $$i_{2}$$ is steady state (at $$t = \infty)$$ current through the battery.
1066603_743dc95169f041c18b5033e87eaf0b3d.png
  • $$1.0$$
  • $$0.8$$
  • $$1.2$$
  • $$1.5$$
In a series $$RLC$$ circuit, potential difference across $$R,L$$ and $$C$$ are $$30V,60V$$ and $$100V$$ respectively as shown in figure. The emf of source (in volts)is:
1079357_84a0a1b2fea344e88fcc7576f24225b7.png
  • $$190$$
  • $$70$$
  • $$50$$
  • $$40$$
A condenser of capacity $$ 20 \mu F$$ is first charged and then discharged through a $$10 mH $$ inductance. Neglecting the resistance of the coil, the frequency of the resulting vibrations will be
  • $$356$$ cycle/s
  • $$35.6$$ cycle/s
  • $$356 \times 10^3 $$ cycle/s
  • $$3.56$$ cycle/s
An $$LCR$$ series circuit with $$R=100\Omega$$ is connected to a $$200\ V,50\ Hz$$ a.c source. When only the capacitance is removed, the current leads the voltage by $$60^{o}$$. When only the inductance is removed, the current leads the voltage by $$60^{o}$$. The current in the circuit is :
  • $$2A$$
  • $$1A$$
  • $$\dfrac {\sqrt {3}}{2}A$$
  • $$\dfrac {2}{\sqrt {3}}A$$
In an LCR circuit, the resonating frequency is $$500$$ $$kH_z$$. If the value of $$L$$ is doubled and value of $$C$$ is decreased to $$\cfrac{1}{8}$$ times of its initial values, then the new resonating frequency in $$kH_z$$ will be
  • $$250$$
  • $$500$$
  • $$1000$$
  • $$2000$$
A coil has resistance $$30 \ ohm $$ and inductive reactance $$ 20 \ ohm$$ at 50 Hz frequency. If an ac source of 200 V,100 Hz is connected across the coil, the current in the coil will be
  • $$ 20\sqrt 13 A$$
  • 2.0 A
  • 4.0 A
  • none
In L-C oscillation if frequency of oscillation of charge is $$f$$, then frequency of oscillation of magnetic energy is
  • $$f$$
  • $$2f$$
  • $$\cfrac{f}{2}$$
  • $$4f$$
An inductor of inductance $$2.0$$ $$H$$ and a resistor of resistance $$10$$ $$\Omega $$ are connected senes to a battery of EMF $$20$$ $$V$$ in a circuit as shown.The key $${ K }_{ 1 }$$ been kept closed for a long time. Then at $$t$$ = $$0$$ , $${ K }_{ 1 }$$i s opened and key $${ K }_{ 2 }$$ is closed simultaneously, The rate of decrease of current in the circuit at $$t$$ = $$1.0 s$$ wili be ($${ e }^{ 5 }$$ = $$150$$)

1118418_ac7f5858d94b45dfa3934fa1c534ad32.png
  • $$\dfrac { 1 }{ 15 } $$ $$A/s$$
  • $$\dfrac { 2 }{ 15 } $$ $$A/s$$
  • $$\dfrac { 1 }{ 5 } $$ $$A/s$$
  • $$\dfrac { 4 }{ 15 } $$ $$A/s$$
A capacitor of capacitance $$C$$ has initial charge $${ Q }_{ 0 }$$ and connected to an inductor of inductance $$L$$ as shown. At $$t=0$$ switch $$S$$ is closed. The current through the inductor when energy in the capacitor is three tirnes the energy of inductor is 

1113299_63cdd99319a949819c58ad71e3fd1a77.png
  • $$\dfrac { { Q }_{ 0 } }{ 2\sqrt { LC } }$$
  • $$\dfrac { { Q }_{ 0 } }{ \sqrt { LC } }$$
  • $$\dfrac { 2{ Q }_{ 0 } }{ \sqrt { LC } } $$
  • $$\dfrac { 4{ Q }_{ 0 } }{ \sqrt { LC } } $$
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