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question_answer1)
If an LCR series circuit is connected to an ac source, then at resonance the
A)
voltage across R is zero done
clear
B)
voltage across R equals the applied voltage done
clear
C)
voltage across C is zero done
clear
D)
voltage across L equals the applied voltage done
clear
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question_answer2)
Of the following about capacitive reactance which is correct?
A)
The reactance of the capacitor is directly proportional to its ability to store charge done
clear
B)
Capacitive reactance is inversely proportional to the frequency of the current done
clear
C)
Capacitive reactance is measured in farad done
clear
D)
The reactance of a capacitor in an A.C. circuit is similar to the resistance of a capacitor in a D.C. circuit done
clear
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question_answer3)
Which one of the following curves represents the variation of impedance (Z) with frequency f in series LCR circuit?
A)
B)
C)
D)
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question_answer4)
The power factor in a circuit connected to an A.C. The value of power factor is
A)
unity when the circuit contains an ideal inductance only done
clear
B)
unity when the circuit contains an ideal resistance only done
clear
C)
zero when the circuit contains an ideal resistance only done
clear
D)
unity when the circuit contains an ideal capacitance only done
clear
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question_answer5)
Which of the following graphs represents the correct variation of capacitive reactance \[{{X}_{C}}\] with frequency v?
A)
B)
C)
D)
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question_answer6)
Current in an ac circuit is given by\[i=3\,\sin \,\omega t+4\,\cos \,\omega t\] then
A)
rms value of current is 5 A done
clear
B)
mean value of this current in one half period will be \[6/\pi \] done
clear
C)
if voltage applied is \[V={{V}_{m\,}}\sin \,\omega t\] then the circuit must be containing resistance and capacitance. done
clear
D)
if voltage applied is \[V={{V}_{m}}\,\sin \,\omega t\], the circuit may contain resistance and inductance. done
clear
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question_answer7)
If we increase the driving frequency in a circuit with a purely capacitive load, then
A)
amplitude\[{{V}_{C}}\]increases done
clear
B)
amplitude\[{{V}_{C}}\]decreases done
clear
C)
amplitude\[{{i}_{C}}\]increases done
clear
D)
amplitude\[{{i}_{C}}\]decreases done
clear
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question_answer8)
If a direct current of value ampere is superimposed on an alternative current\[I=b\,\sin \,\omega t\] flowing through a wire, what is the effective value of the resulting current in the circuit?
A)
\[{{\left[ {{a}^{2}}-\frac{1}{2}{{b}^{2}} \right]}^{1/2}}\] done
clear
B)
\[{{\left[ {{a}^{2}}+{{b}^{2}} \right]}^{1/2}}\] done
clear
C)
\[{{\left[ \frac{{{a}^{2}}}{2}+{{b}^{2}} \right]}^{1/2}}\] done
clear
D)
\[{{\left[ {{a}^{2}}+\frac{{{b}^{2}}}{2} \right]}^{1/2}}\] done
clear
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question_answer9)
In a series LCR circuit, the difference of the frequencies at which current amplitude falls to\[\frac{1}{\sqrt{2}}\] of the current amplitude at resonance is
A)
\[\frac{R}{2\pi L}\] done
clear
B)
\[\frac{R}{\pi L}\] done
clear
C)
\[\frac{2R}{\pi L}\] done
clear
D)
\[\frac{3R}{2\pi L}\] done
clear
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question_answer10)
If\[{{i}_{1}}=3\,\sin \,\omega t\]and\[{{i}_{2}}=4\,\cos \,\omega t\], then\[{{i}_{3}}\]is
A)
\[5\,\sin \,(\omega t+{{53}^{o}})\] done
clear
B)
\[5\,\sin \,(\omega t+{{37}^{o}})\] done
clear
C)
\[5\,\sin \,(\omega t+{{45}^{o}})\] done
clear
D)
\[5\,\cos \,(\omega t+{{53}^{o}})\] done
clear
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question_answer11)
A sinusoidal voltage V(t) = 100 sin (500t) is applied across a pure inductance of L=0.02H. The current through the coil is:
A)
\[10\,\cos \,(500\,t)\] done
clear
B)
\[-10\,\cos \,(500\,t)\] done
clear
C)
\[10\,\sin \,(500\,t)\] done
clear
D)
\[-10\,\sin \,(500\,t)\] done
clear
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question_answer12)
Figure shows one cycle of an alternating current with the segments AB, BC, CD, DE being symmetrical and parabolic. The root mean square value of this current over one cycle is x mA, find x.
A)
1mA done
clear
B)
2mA done
clear
C)
3mA done
clear
D)
4mA done
clear
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question_answer13)
In given circuit capacitor initially uncharged. Now at t=0 switch S is closed then current given by source at any time t is
A)
\[\frac{2}{R}\left( 1-{{e}^{\frac{-2t}{CR}}} \right)\] done
clear
B)
\[\frac{\varepsilon }{2R}\left( 1+{{e}^{\frac{-2t}{CR}}} \right)\] done
clear
C)
\[\frac{\varepsilon }{2R}\left( 1-{{e}^{\frac{-2t}{CR}}} \right)\] done
clear
D)
\[\frac{2\varepsilon }{R}\left( 1-{{e}^{\frac{-2t}{CR}}} \right)\] done
clear
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question_answer14)
The transformer voltage induced in the secondary coil of a transformer is mainly due to
A)
a varying electric field done
clear
B)
a varying magnetic field done
clear
C)
the vibrations of the primary coil done
clear
D)
the iron core of the transformer done
clear
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question_answer15)
A coil of inductance 8.4 mH and resistance \[6\,\Omega \] is connected to a 12 V battery. The current in the coil is 1.0 A at approximately the time
A)
500s done
clear
B)
25s done
clear
C)
35ms done
clear
D)
1ms done
clear
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question_answer16)
Resonance frequency of a circuit is f. If the capacitance is made 4 times the initial value, the resonance frequency will become :
A)
\[f/2\] done
clear
B)
2f done
clear
C)
f done
clear
D)
f/4 done
clear
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question_answer17)
The current (7) in the inductance is varying with time according to the plot shown in figure.
Which one of the following is the correct variation of voltage with time in the coil?
A)
B)
C)
D)
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question_answer18)
The voltage of an ac supply varies with time (t) I as\[V=120\,\sin \,100\pi \,t\,\cos \,100\pi t\]. The maximum voltage and frequency respectively are
A)
120 volts, 100 Hz done
clear
B)
\[\frac{120}{\sqrt{2}}volts,\,\,100Hz\] done
clear
C)
60 volts, 200 Hz done
clear
D)
60 volts, 100 Hz done
clear
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question_answer19)
The equation of AC voltage is\[E=220\,\sin \,(\omega t+\pi /6)\] and the A.C. current\[I=10\,\sin \,(\omega t+\pi /6)\]. The average power dissipated is
A)
150 W done
clear
B)
550 W done
clear
C)
250 W done
clear
D)
50 W done
clear
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question_answer20)
In an L-R circuit, the value of L is \[(0.4/\pi )\]henry and the value of R is 30 ohm. If in the circuit, an alternating emfof200 volt at 50 cycles per second is connected, the impedance of the circuit and current will be:
A)
11.4 ohm, 17.5 ampere done
clear
B)
30.7 ohm, 6.5 ampere done
clear
C)
40.4 ohm, 5 ampere done
clear
D)
50 ohm, 4 ampere. done
clear
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question_answer21)
In an ac circuit an alternating voltage e=200 \[\sqrt{2}\,\sin \,100\,t\] volts is connected to a capacitor of capacity \[1\,\mu F\]. The r.m.s. value of the current in the circuit is
A)
10 mA done
clear
B)
100 mA done
clear
C)
200 mA done
clear
D)
20 mA done
clear
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question_answer22)
Determine the rms value of a semi-circular current wave which has a maximum value of a.
A)
\[(1\sqrt{2})a\] done
clear
B)
\[(\sqrt{3/2})a\] done
clear
C)
\[(\sqrt{2/3})a\] done
clear
D)
\[(\sqrt{1/3})a\] done
clear
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question_answer23)
The r.m.s. value of potential difference V shown in the figure is
A)
\[{{V}_{0}}\] done
clear
B)
\[{{V}_{0}}/\sqrt{2}\] done
clear
C)
\[{{V}_{0}}/2\] done
clear
D)
\[{{V}_{0}}/\sqrt{3}\] done
clear
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question_answer24)
The equation of alternating current is : |
\[I=50\sqrt{2}\,\sin \,400\pi t\,amp\]. Then the frequency and root mean square of current are respectively |
A)
\[200\text{ }Hz,\text{ }50\text{ }amp\] done
clear
B)
\[400\pi \,Hz,\,\,50\sqrt{2}\,\,\,amp\] done
clear
C)
\[200\,Hz,\,\,\,50\sqrt{2}\,\,amp\] done
clear
D)
\[50\text{ }Hz,\text{ }200\text{ }amp\] done
clear
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question_answer25)
A coil has resistance 30 ohm and inductive reactance 20 ohm at 50 Hz frequency If an ac source, of 200 volt, 100 Hz, is connected across the coil, the current in the coil will be
A)
4.0 A done
clear
B)
8.0 A done
clear
C)
\[\frac{20}{\sqrt{13}}\,A\] done
clear
D)
2.0 A done
clear
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question_answer26)
A small signal voltage\[V(t)={{V}_{0}}\,\sin \,\omega t\]is applied across an ideal capacitor C:
A)
Current I (t), lags voltage V (t) by \[90{}^\circ \]. done
clear
B)
Over a fall cycle the capacitor C does not consume any energy from the voltage source. done
clear
C)
Current I (t) is in phase with voltage V (t). done
clear
D)
Current I (t) leads voltage V (t) by \[180{}^\circ \]. done
clear
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question_answer27)
An ac voltage is applied to a resistance R and an inductor L in series. If R and the inductive reactance are both equal to \[3\,\Omega \], the phase difference between the applied voltage and the current in the circuit is
A)
\[\pi /6\] done
clear
B)
\[\pi /4\] done
clear
C)
\[\pi /2\] done
clear
D)
zero done
clear
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question_answer28)
The voltage time (V-t) graph for triangular wave having peak value \[{{V}_{0}}\] is as shown in figure. |
The rms value of V in time interval from t=0 to T/4 is |
A)
\[\frac{{{V}_{0}}}{\sqrt{3}}\] done
clear
B)
\[\frac{{{V}_{0}}}{2}\] done
clear
C)
\[\frac{{{V}_{0}}}{\sqrt{2}}\] done
clear
D)
\[\frac{{{V}_{0}}}{3}\] done
clear
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question_answer29)
An inductor 20 mH, a capacitor \[50\,\mu F\]and a resistor \[40\Omega \] are connected in series across a source of emf V=10 sin 340 t. The power loss in A.C. circuit is:
A)
0.51 W done
clear
B)
0.67 W done
clear
C)
0.76 W done
clear
D)
0.89 W done
clear
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question_answer30)
A series R-C circuit is connected to an alternating voltage source. Consider two situations: |
When capacitor is air filled. |
When capacitor is mica filled. |
Current through resistor is i and voltage across capacitor is V then: |
A)
\[{{V}_{a}}>{{V}_{b}}\] done
clear
B)
\[{{i}_{a}}>{{i}_{b}}\] done
clear
C)
\[{{V}_{a}}={{V}_{b}}\] done
clear
D)
\[{{V}_{a}}<{{V}_{b}}\] done
clear
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question_answer31)
Find the current passing through battery immediately after key (K) is closed. It is given that initially all the capacitors are uncharged. (given that \[R=6\,\Omega \] and \[C=4\mu F\])
A)
1 A done
clear
B)
5 A done
clear
C)
3 A done
clear
D)
2 A done
clear
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question_answer32)
A resistance 'R' draws power 'P' when connected to an AC source. If an inductance is now placed in series with the resistance, such that the impedance of the circuit becomes 'Z', the power drawn will be
A)
\[P\sqrt{\frac{R}{Z}}\] done
clear
B)
\[P\left( \frac{R}{Z} \right)\] done
clear
C)
P done
clear
D)
\[P{{\left( \frac{R}{Z} \right)}^{2}}\] done
clear
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question_answer33)
A condenser of capacity C is charged to a potential difference of \[{{V}_{1}}\]. The plates of the condenser are then connected to an ideal inductor of inductance L. The current through the inductor when the potential difference across the condenser reduces to \[{{V}_{2}}\] is
A)
\[{{\left( \frac{C(V_{1}^{2}-V_{2}^{2})}{L} \right)}^{1/2}}\] done
clear
B)
\[{{\left( \frac{C{{({{V}_{1}}-{{V}_{2}})}^{2}}}{L} \right)}^{1/2}}\] done
clear
C)
\[\frac{C(V_{1}^{2}-V_{2}^{2})}{L}\] done
clear
D)
\[\frac{C({{V}_{1}}-{{V}_{2}})}{L}\] done
clear
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question_answer34)
For the circuit as shown in figure; the applied Current in A.C. circuit is zero ampere and\[{{I}_{C}}=10A\]. Then the magnitude of current \[{{I}_{L}}\]is
A)
4 A done
clear
B)
10 A done
clear
C)
5 A done
clear
D)
undefined done
clear
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question_answer35)
What is the value of inductance L for which the current is maximum in a series LCR circuit with \[C=10\mu F\] and \[\omega =1000{{s}^{-1}}\]?
A)
1 mH done
clear
B)
cannot be calculated unless R is known done
clear
C)
10 mH done
clear
D)
100 mH done
clear
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question_answer36)
In the circuit shown, the symbols have their usual meanings. The cell has emf E. X is initially joined to V for a long time. Then, disjoined to Z The maximum charge on C at any later time will be
A)
\[\frac{E}{R\sqrt{LC}}\] done
clear
B)
\[\frac{ER}{2\sqrt{LC}}\] done
clear
C)
\[\frac{E\sqrt{LC}}{2R}\] done
clear
D)
\[\frac{E\sqrt{LC}}{R}\] done
clear
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question_answer37)
A coil of inductive reactance \[31\,\Omega \]has a resistance of \[8\,\Omega \]. It is placed in series with a condenser of capacitive reactance \[25\,\Omega \]. The combination is connected to an a.c. source of 110 volt. The power factor of the circuit is
A)
0.64 done
clear
B)
0.80 done
clear
C)
0.33 done
clear
D)
0.56 done
clear
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question_answer38)
The two capacitors, shown in the circuit, are initially uncharged and the cell is ideal. The switch S is closed at t=0. Which of the following functions represents the current i(t) through the cell as a function of time? Here\[{{i}_{0}},\,{{i}_{1}},\,{{i}_{2}}\]are constants.
A)
\[i(t)={{i}_{0}}+{{i}_{1}}{{e}^{-t/\tau }}\]; \[\tau =3C\times \frac{R}{3}\] done
clear
B)
\[i(t)={{i}_{0}}+{{i}_{1}}{{e}^{-t/\tau }}+{{i}_{2}}{{e}^{-t/2\tau }}\]; \[\tau =RC\] done
clear
C)
\[i(t)={{i}_{1}}+{{i}_{1}}{{e}^{-t/\tau }}\]; \[\tau =3C\times \frac{R}{3}\] done
clear
D)
\[i(t)={{i}_{0}}+{{i}_{1}}{{e}^{-t/\tau }}\]; \[\tau =3RC\] done
clear
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question_answer39)
A coil of 40 henry inductance is connected in series with a resistance of 8 ohm and the combination is joined to the terminals of a 2 volt battery. The time constant of the circuit is
A)
20 seconds done
clear
B)
5 seconds done
clear
C)
1/5 seconds done
clear
D)
40 seconds done
clear
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question_answer40)
A resistor and an inductor are connected to an ac supply of 120 V and 50 Hz. The current in the circuit is 3 A. If the power consumed in the circuit is 108 W, then the resistance in the circuit is
A)
\[12\,\Omega \] done
clear
B)
\[40\,\Omega \] done
clear
C)
\[\sqrt{(52\times 25)}\Omega \] done
clear
D)
\[360\,\Omega \] done
clear
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question_answer41)
A short-circuited coil is placed in a time-varying magnetic field. Electrical power is dissipated due to the current induced in the coil. If the number of turns were to be quadrupled and the wire radius halved, the electrical power dissipated would be
A)
equal done
clear
B)
the same done
clear
C)
doubled done
clear
D)
quadrupled done
clear
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question_answer42)
An LCR series circuit with \[100\,\Omega \] resistance is connected to an AC source of 200 V and angular frequency 300 radians per second. When only the capacitance is removed, the current lags behind the voltage by \[60{}^\circ \]. When only the inductance is removed, the current leads the voltage by \[60{}^\circ \]. Then the current and power dissipated in LCR circuit are respectively
A)
1A, 200 watt done
clear
B)
1A, 400 watt done
clear
C)
2A, 200 watt done
clear
D)
2A, 400 watt done
clear
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question_answer43)
In the circuits and switches\[{{S}_{1}}\]and\[{{S}_{2}}\]are S closed at t=0 and are kept closed for a long time The variation of current in the two circuits for\[t\ge 0\]are roughly shown by figure (figures are schematic and not drawn to scale):
A)
B)
C)
D)
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question_answer44)
A coil has an inductance of 0.7 henry and is joined in series with a resistance of \[220\,\Omega \]. When the alternating emf of 220 V at 50 Hz is applied to it then the phase through which current lags behind the applied emf and the watt less component of current in the circuit will be respectively
A)
\[30{}^\circ ,\text{ }1\text{ }A\] done
clear
B)
\[45{}^\circ ,\text{ }0.5\text{ }A\] done
clear
C)
\[60{}^\circ ,\text{ }1.5\text{ }A\] done
clear
D)
None of these done
clear
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question_answer45)
In an L-C circuit shown in the figure, C=1F, L=4H at time t=0, charge in the capacitor is 4C and it is decreasing at a rate of\[\sqrt{5}\,C/s\]. Choose the correct statements.
A)
maximum charge in the capacitor can be 6C done
clear
B)
maximum charge in the capacitor can be 8C done
clear
C)
charge in the capacitor will be maximum after time \[2\,{{\sin }^{-1}}\](2/3) sec done
clear
D)
None of these done
clear
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question_answer46)
Charges on the capacitors in four oscillating LC circuits vary as follows: (1) q=2 cos 4t, (2) q =4 cos t, (3) q = 3 cos 4t, (4) q = 4 cos 2t, with q in coulomb and t in second. In which circuit(s) current amplitude is greatest?
A)
(1) done
clear
B)
(2) done
clear
C)
(3) done
clear
D)
(4) done
clear
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question_answer47)
Figure shows a source of alternating voltage connected to a capacitor and resistor. Which of the following phasor diagrams correctly secrobes the phase relationship between\[{{I}_{c}}\], the current between the source and the capacitor, and\[{{I}_{R}}\], the current in the resistor?
A)
\[\begin{align} & \xrightarrow{{{I}_{c}}} \\ & \xrightarrow[{{I}_{R}}]{} \\ \end{align}\] done
clear
B)
\[\xleftarrow{{{I}_{C}}}\xrightarrow{{{I}_{R}}}\] done
clear
C)
D)
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question_answer48)
A capacitor of\[10\,\mu F\]and an inductor of 1 H are joined in series. An ac of 50 Hz is applied to this combination. What is the impedance of the combination?
A)
\[\frac{5({{\pi }^{2}}-5)}{\pi }\Omega \] done
clear
B)
\[\frac{{{10}^{2}}(10-{{\pi }^{2}})}{\pi }\,\Omega \] done
clear
C)
\[\frac{10({{\pi }^{2}}-5)}{\pi }\,\Omega \] done
clear
D)
\[\frac{{{5}^{2}}(10-{{\pi }^{2}})}{\pi }\Omega \] done
clear
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question_answer49)
What is the amount of power delivered by the ac source in the circuit shown (in watts).
A)
500 watt done
clear
B)
1014 watt done
clear
C)
1514 watt done
clear
D)
2013 watt done
clear
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question_answer50)
The current in an L-R circuit builds up to\[{{(3/4)}^{th}}\]of its steady state value in 4 seconds. The time constant of this circuit is
A)
\[\frac{1}{ln\,\,2}\sec \] done
clear
B)
\[\frac{2}{ln\,\,2}\sec \] done
clear
C)
\[\frac{3}{ln\,\,2}\sec \] done
clear
D)
\[\frac{4}{ln\,\,2}\sec \] done
clear
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question_answer51)
A resistor of resistance R, capacitor of capacitance C and inductor of inductance L are connected in parallel to AC power source of voltage \[{{\varepsilon }_{0}}\,\sin \,\omega t\]. The maximum current through the resistance is half of the maximum current through the power source. Then value of R is
A)
\[\frac{\sqrt{3}}{\left| \left. \omega C-\frac{1}{\omega L} \right| \right.}\] done
clear
B)
\[\sqrt{3}\left. \left| \frac{1}{\omega C}-\omega L \right. \right|\] done
clear
C)
\[\sqrt{5}\left. \left| \frac{1}{\omega C}-\omega L \right. \right|\] done
clear
D)
None of these done
clear
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question_answer52)
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 sources is 100 V, the \[{{V}_{R}}\] is close to:
A)
50V done
clear
B)
70V done
clear
C)
90V done
clear
D)
100V done
clear
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question_answer53)
Time constant of L-R circuit will be
A)
\[\frac{L}{R}\] done
clear
B)
\[\frac{2L}{R}\] done
clear
C)
\[\frac{L}{2R}\] done
clear
D)
None of these done
clear
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question_answer54)
A series LR circuit is connected to an ac source of frequency \[\omega \] and the inductive reactance is equal to 2R. A capacitance of capacitive reactance equal to R is added in series with L and R. The ratio of the new power factor to the
A)
\[\sqrt{\frac{2}{3}}\] done
clear
B)
\[\sqrt{\frac{2}{5}}\] done
clear
C)
\[\sqrt{\frac{3}{2}}\] done
clear
D)
\[\sqrt{\frac{5}{2}}\] done
clear
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question_answer55)
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 the circuit is closed at t=0. At what time is the energy stored completely magnetic?
A)
t=0 done
clear
B)
t=1.57 ms done
clear
C)
t=3.14 ms done
clear
D)
t= 6.28 ms done
clear
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question_answer56)
An inductor \[20\times {{10}^{-3}}\] Henry, a capacitor \[100\,\mu F\]and a resistor \[50\,\Omega \] are connected in series across a source of EMF V=10 sin 314t. If resistance is removed from the circuit and the value of inductance is doubled, then the variation of current with time in the new circuit is -
A)
\[0.52\text{ }cos\text{ }314t\] done
clear
B)
\[0.52\text{ }sin\text{ }314t\] done
clear
C)
\[0.52\,\sin \,(314t+\pi /3)\] done
clear
D)
None of these done
clear
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question_answer57)
In a LCR circuit capacitance is changed from C to 1C. For the resonant frequency to remain unchanged, the inductance should be change from L to
A)
4L done
clear
B)
2L done
clear
C)
\[L/2\] done
clear
D)
\[L/4\] done
clear
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question_answer58)
As shown in figure, value of inductive reactance \[{{X}_{L}}\] will be if source voltage is 100 volt
A)
\[40\,\Omega \] done
clear
B)
\[30\,\Omega \] done
clear
C)
\[50\,\Omega \] done
clear
D)
can have any value done
clear
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question_answer59)
In a series L-C-R circuit, \[C={{10}^{-11}}\] Farad, \[L={{10}^{-5}}\] Henry and R=100 Ohm, when a constant D.C. voltage E is applied to the circuit, the capacitor acquires a charge \[{{10}^{-9}}\,C\]. The D.C. source is replaced by a sinusoidal voltage source in which the peak voltage \[{{E}_{0}}\]is equal to the constant D.C. voltage E. At resonance the peak value of the charge acquired by the capacitor will be:
A)
\[{{10}^{-15}}\,C\] done
clear
B)
\[{{10}^{-6}}\,C\] done
clear
C)
\[{{10}^{-10}}\,C\] done
clear
D)
\[{{10}^{-8}}\,C\] done
clear
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question_answer60)
In a uniform magnetic field of induction B a wire in the form of a semicircle of radius r rotates about the diameter of the circle with an angular frequency \[\omega \]. The axis of rotation is perpendicular to the field. If the total resistance of the circuit is R, the mean power generated per period of rotation is
A)
\[\frac{{{(B\pi r\omega )}^{2}}}{2R}\] done
clear
B)
\[\frac{{{(B\pi {{r}^{2}}\omega )}^{2}}}{8R}\] done
clear
C)
\[\frac{B\pi {{r}^{2}}\omega }{2R}\] done
clear
D)
\[\frac{{{(B\pi r{{\omega }^{2}})}^{2}}}{8R}\] done
clear
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question_answer61)
An ac source of angular frequency co 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. Then the ratio of reactance to resistance at the original frequency \[\omega \]is
A)
\[\sqrt{3/5}\] done
clear
B)
\[\sqrt{5/3}\] done
clear
C)
\[\sqrt{2/3}\] done
clear
D)
\[\sqrt{3/2}\] done
clear
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question_answer62)
In the LC circuit, the current is in the direction shown and the charges on the capacitor plates have the signs shown. At this time,
A)
I is increasing and Q is increasing done
clear
B)
I is increasing and Q is decreasing done
clear
C)
I is decreasing and Q is increasing done
clear
D)
I is decreasing and Q is decreasing done
clear
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question_answer63)
An LCR circuit contains resistance of 100 ohm and a supply of 200 volt at 300 radian angular frequency If only capacitance is taken out from the circuit and the rest of the circuit is joined, current lags behind the voltage by \[60{}^\circ \].If on the other hand, only inductor is taken out, the current leads by \[60{}^\circ \]with the applied voltage. The current flowing in the circuit is:
A)
1 A done
clear
B)
1.5 A done
clear
C)
2 A done
clear
D)
2.5 A done
clear
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question_answer64)
In an electrical circuit R, L, C and an a.c. voltage source are all connected in series. When L is removed from the circuit, the phase difference between the voltage the current in the circuit is\[\pi /3\]. If instead, C is removed from the circuit, the phase difference is again \[\pi /3\]. The power factor of the circuit is :
A)
\[1/2\] done
clear
B)
\[1/\sqrt{2}\] done
clear
C)
1 done
clear
D)
\[\sqrt{3}/2\] done
clear
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question_answer65)
In given RC circuit, capacitance of capacitor \[{{C}_{1}}=3\mu F\]and \[{{C}_{2}}=1\mu F\]. It is given that time constant of circuit between A and B is 3 millisecond. Value of R will be
A)
\[1\,\Omega \] done
clear
B)
\[10\,\Omega \] done
clear
C)
\[100\,\Omega \] done
clear
D)
\[1000\,\Omega \] done
clear
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question_answer66)
The circuit shown has been operating for a long time. The instant after the switch in the circuit labeled S is opened, what is the voltage across the inductor \[{{V}_{L}}\] and which labeled point (A or B) of the inductor is at a higher potential? Take \[{{R}_{1}}=4.0\,\Omega \], \[{{R}_{2}}=8.0\,\Omega \] and \[L=2.5\,H\].
A)
\[{{V}_{L}}=12V\], point A is at the higher potential done
clear
B)
\[{{V}_{L}}=12V\], point B is at the higher potential done
clear
C)
\[{{V}_{L}}=6V\], point A is at the higher potential done
clear
D)
\[{{V}_{L}}=6V\], point B is at the higher potential done
clear
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question_answer67)
In the circuit shown below, the key K is closed at t=0. The current through the battery is
A)
\[\frac{V{{R}_{1}}{{R}_{2}}}{\sqrt{R_{1}^{2}+R_{2}^{2}}}\] at t=0 and \[\frac{V}{{{R}_{2}}}\] at \[t=\infty \] done
clear
B)
\[\frac{V}{{{R}_{2}}}\] at t=0 and \[\frac{V({{R}_{1}}+{{R}_{2}})}{{{R}_{1}}{{R}_{2}}}\] at \[t=\infty \] done
clear
C)
\[\frac{V}{{{R}_{2}}}\] at t=0 and \[\frac{V{{R}_{1}}{{R}_{2}}}{\sqrt{R_{1}^{2}+R_{2}^{2}}}\] at \[t=\infty \] done
clear
D)
\[\frac{V({{R}_{1}}+{{R}_{2}})}{{{R}_{1}}{{R}_{2}}}\] at t=0 and \[\frac{V}{{{R}_{2}}}\] at \[t=\infty \] done
clear
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question_answer68)
An arc lamp requires a direct current of 10 A at 80 V to function. If it is connected to a 220 V (rms),50 Hz AC supply, the series inductor needed for it to work is close to :
A)
0.044 H done
clear
B)
0.065 H done
clear
C)
80 H done
clear
D)
0.08 H done
clear
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question_answer69)
In a series LCR circuit \[R=200\Omega \] and the voltage and the frequency of the main supply is 220V and 50 Hz respectively. On taking out the capacitance from the circuit the current lags behind the voltage by \[30{}^\circ \]. On taking out the inductor from the circuit the current leads the voltage by \[30{}^\circ \]. The power dissipated in the LCR circuit is
A)
305 W done
clear
B)
210W done
clear
C)
Zero W done
clear
D)
242 W done
clear
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question_answer70)
A fully charged capacitor C with initial charge \[{{q}_{0}}\] is connected to a coil of self-inductance L at\[t=0.\]The time at which the energy is stored equally between the electric and the magnetic fields is:
A)
\[\frac{\pi }{4}\sqrt{LC}\] done
clear
B)
\[2\pi \sqrt{LC}\] done
clear
C)
\[\sqrt{LC}\] done
clear
D)
\[\pi \sqrt{LC}\] done
clear
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question_answer71)
An inductor (L=0.03 H) and a resistor\[(R=0.15k\Omega )\]are connected in series to a battery of 15V emf in a circuit shown below. The key \[{{K}_{1}}\] has been kept closed for a long time. Then at t= 0, \[{{K}_{1}}\] is opened and key \[{{K}_{2}}\], is closed simultaneously. At f = 1 ms, the current in the circuit will be : \[({{e}^{5}}\cong 150)\]
A)
6.7 Ma done
clear
B)
0.67 mA done
clear
C)
100 mA done
clear
D)
67 mA done
clear
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question_answer72)
A resistor 'R' and \[2\mu F\] capacitor in series is connected through a switch to 200 V direct supply. Across the capacitor is a neon bulb that lights up at 120 V. Calculate the value of R to make the bulb light up 5 s after the switch has been closed, \[(lo{{g}_{10}}2.5=0.4)\]
A)
\[1.7\times {{10}^{5}}\Omega \] done
clear
B)
\[2.7\times {{10}^{6}}\Omega \] done
clear
C)
\[3.3\times {{10}^{7}}\Omega \] done
clear
D)
\[1.3\times {{10}^{4}}\,\Omega \] done
clear
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question_answer73)
In the circuit shown here, the point 'C' is kept connected to point 'A' till the current flowing through the circuit becomes constant. Afterward, suddenly, point 'C' is disconnected from point 'A' and connected to point 'B' at time t=0. Ratio of the voltage across resistance and the inductor at t = L/R will be equal to:
A)
\[\frac{e}{1-e}\] done
clear
B)
1 done
clear
C)
- 1 done
clear
D)
\[\frac{1-e}{e}\] done
clear
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question_answer74)
Combination of two identical capacitors, a resistor R and a dc voltage source of voltage 6V is used in an experiment on a (C-R) circuit. It is found that for a parallel combination of the capacitor the time in which the voltage of the fully charged combination reduces to half its original voltage is 10 second. For series combination the time needed for reducing the voltage of the fully charged series combination by half is
A)
10 second done
clear
B)
5 second done
clear
C)
2.5 second done
clear
D)
20 second done
clear
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question_answer75)
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 statements is correct?
A)
At, t=0, q=CV (1-e) done
clear
B)
At,\[t=\tau \], \[q=CV/2\] done
clear
C)
At, \[t=2\tau \], \[q=CV(1-{{e}^{-e}})\] done
clear
D)
At, \[t=2\tau \], \[q=CV(1-{{e}^{-1}})\] done
clear
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question_answer76)
Figure shows an iron - cored transformer assumed to be 100% efficient. The ratio olf the secondary turns to the primary turns is 1:20.
A 240 V ac supply is connected to the primary coil and a 6 W resistor is corrected to the secondary coil. What is the current in the primary coil?
A)
0.10 A done
clear
B)
0.14 A done
clear
C)
2 A done
clear
D)
40 A done
clear
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question_answer77)
A step down transformer is connected to 2400 volts line and 80 amperes of current is found to flow in output load. The ratio of the turns in primary and secondary coil is 20:1. If transformer efficiency is 100%, then the current flowing in the primary coil will be
A)
1600 amp done
clear
B)
20 amp done
clear
C)
4 amp done
clear
D)
1.5 amp done
clear
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question_answer78)
At t < 0, the capacitor is charged and the switch is opened. At t=0 the switch is closed. The shortest time T at which the charge on the capacitor will be zero is given by
A)
\[\pi \sqrt{LC}\] done
clear
B)
\[\frac{3}{2}\pi \sqrt{LC}\,\] done
clear
C)
\[\frac{\pi }{2}\sqrt{LC}\,\] done
clear
D)
\[2\pi \sqrt{LC}\,\] done
clear
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question_answer79)
The primary and secondary coil of a transformer have 50 and 1500 turns respectively. If the magnetic flux \[\phi \] linked with the primary coil is given by \[\phi ={{\phi }_{0}}+4t\], where \[\phi \] is in webers, t is time in seconds and \[{{\phi }_{0}}\] is a constant, the output voltage across the secondary con is
A)
120 volts done
clear
B)
220 volts done
clear
C)
30 volts done
clear
D)
90 volts done
clear
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question_answer80)
An ideal efficient transformer has a primary power input of 10 kW. The secondary current when the transformer is on load is 25 A. If the primary: secondary turns ratio is 8 : 1, then the potential difference applied to the primary coil is
A)
\[\frac{{{10}^{4}}\times {{8}^{2}}}{25}V\] done
clear
B)
\[\frac{{{10}^{4}}\times 8}{25}V\] done
clear
C)
\[\frac{{{10}^{4}}}{25\times 8}V\] done
clear
D)
\[\frac{{{10}^{4}}}{25\times {{8}^{2}}}V\] done
clear
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question_answer81)
A transformer is used to light a 140 W, 24 V bulb from a 240 V a.c. mains. The current in the main cable is 0.7 A. The efficiency of the transformer is
A)
\[63.8\text{ }%\] done
clear
B)
\[83.3\text{ }%\] done
clear
C)
\[16.7%\] done
clear
D)
\[36.2%\] done
clear
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question_answer82)
In an ideal transformer, the voltage and the current in the primary coil are 200 V and 2 A, respectively. If the voltage in the secondary coil is 2000 V, the value of current in the secondary coil will be
A)
0.2 A done
clear
B)
2 A done
clear
C)
10 A done
clear
D)
20 A done
clear
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question_answer83)
In an oscillating LC circuit with L = 50 mH and\[C=4.0\,\mu F\], the current is initially a maximum. How long will it take before the capacitor is fully discharged for the first time:
A)
\[7\times {{10}^{-4}}\,s\] done
clear
B)
\[14\times {{10}^{-4}}\,s\] done
clear
C)
\[28\times {{10}^{-4}}\,s\] done
clear
D)
none of these done
clear
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question_answer84)
The primary of a winding transformer has 400 turns while the secondary has 2000 turns. If the power output from the secondary at 1000 V is 12 kW, what is the primary voltage?
A)
200V done
clear
B)
300V done
clear
C)
400V done
clear
D)
500V done
clear
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question_answer85)
Figure shows three oscillating LC circuit with identical inductors and capacitors. If\[{{t}_{1}}\], \[{{t}_{2}}\], \[{{t}_{3}}\] are the time taken by the circuits I, II, III for fully discharge, then
A)
\[{{t}_{1}}>{{t}_{2}}>{{t}_{3}}\] done
clear
B)
\[{{t}_{1}}<{{t}_{2}}<{{t}_{3}}\] done
clear
C)
\[{{t}_{2}}<{{t}_{1}}<{{t}_{3}}\] done
clear
D)
\[{{t}_{3}}=\sqrt{{{t}_{1}}{{t}_{2}}}\] done
clear
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question_answer86)
The primary of a transformer when connected to a dc battery of 10 volt draws a current of 1 mA. The I number of turns of the primary and secondary windings are 50 and 100 respectively The voltage in the secondary and the current drawn by the circuit in the secondary are respectively
A)
20 V and 0.5 mA done
clear
B)
20 V and 2.0 mA done
clear
C)
10 V and 0.5 mA done
clear
D)
Zero and therefore no current done
clear
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question_answer87)
A transformer having efficiency of 90% is working on 200V and 3kW power supply. If the current in the secondary coil is 6A, the voltage across the secondary coil and the current in the primary coil respectively are:
A)
300V, 15A done
clear
B)
450V, 15A done
clear
C)
450V, 13.5A done
clear
D)
600V, 15A done
clear
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question_answer88)
For long distance transmission, the A.C.is stepped up because of high voltage, the transmission is
A)
faster done
clear
B)
economical done
clear
C)
undamped done
clear
D)
less dangerous done
clear
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question_answer89)
A capacitor in an LC oscillator has a maximum potential difference of 17 V and a maximum energy of \[160\,\mu J\]. When the capacitor has a potential difference of 5V and an energy of \[10\,\mu J,\] what is the energy stored in the magnetic field?
A)
\[10\,\mu J\] done
clear
B)
\[150\,\mu J\] done
clear
C)
\[160\,\mu J\] done
clear
D)
\[170\,\mu J\] done
clear
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question_answer90)
A transformer rated at 10 KW is used to connect a 5 KV transmission line to a 240V circuit. The ratio of turns in the windings of the transformer is:
A)
5 done
clear
B)
20.8 done
clear
C)
104 done
clear
D)
40 done
clear
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question_answer91)
A step up transformer operates on a 230 V line and supplies a current of 2 ampere. The ratio of primary and secondary winding is 1:25. The current in primary is
A)
25 A done
clear
B)
50 A done
clear
C)
15 A done
clear
D)
12.5 A done
clear
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question_answer92)
The tuning circuit of a radio receiver has a resistance of \[50\,\Omega \], an inductor of 10 mH and a variable capacitor. A 1 MHz radio wave produces a potential difference of 0.1 mV. The values of the capacitor to produce resonance is \[(Take\,{{\pi }^{2}}=10)\]
A)
2.5 pF done
clear
B)
5.0 pF done
clear
C)
25 pF done
clear
D)
50 pF done
clear
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question_answer93)
A generator at a utility company produces 100 A of current at 4000 V. The voltage is stepped up to 2, 40, 000V by a transformer before it is sent on a high voltage transmission line. The current in transmission line is
A)
3.67 A done
clear
B)
2.67 A done
clear
C)
1.67 A done
clear
D)
2.40 A done
clear
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question_answer94)
A transistor-oscillator using a resonant circuit with an inductor L (of negligible resistance) and a capacitor C in series produce oscillations of frequency f. If L is doubled and C is changed to 4C, the frequency will be
A)
\[8f\] done
clear
B)
\[f/2\sqrt{2}\] done
clear
C)
\[f/2\] done
clear
D)
\[f/4\] done
clear
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question_answer95)
A 220 volts input is supplied to a transformer. The output circuit draws a current of 2.0 ampere at 440 volts. If the efficiency of the transformer is 80%, the current drawn by the primary windings of the transformer is
A)
3.6 ampere done
clear
B)
2.8 ampere done
clear
C)
2.5 ampere done
clear
D)
5.0 ampere done
clear
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