Correct4
Incorrect-1
The power factor of an AC circuit having resistance {tex} ( R ) {/tex} and inductance {tex} ( L ) {/tex} connected in series and an angular velocity {tex} \omega {/tex} is
{tex} R / \omega L {/tex}
{tex} R / \left( R ^ { 2 } + \omega ^ { 2 } L ^ { 2 } \right) ^ { 1 / 2 } {/tex}
{tex} \omega L / R {/tex}
{tex} R / \left( R ^ { 2 } - \omega ^ { 2 } L ^ { 2 } \right) ^ { 1 / 2 } {/tex}
Correct4
Incorrect-1
A conducting square loop of side {tex} L {/tex} and resistance {tex} R {/tex} moves in its plane with a uniform velocity v perpendicular to one of its sides. A magnetic induction {tex} B {/tex} constant in time and space, pointing perpendicular and into the plane at the loop exists everywhere with half the loop outside the field, as shown in figure. The induced emf is
{tex} zero{/tex}
{tex} R v B {/tex}
{tex} v B L / R {/tex}
{tex} v B I {/tex}
Correct4
Incorrect-1
The inductance between {tex} A {/tex} and {tex} D {/tex} is
{tex} 3.66\ \mathrm { H } {/tex}
{tex} 9\mathrm { H } {/tex}
{tex} 0.66\mathrm { H } {/tex}
{tex} 1 \mathrm { H } {/tex}
Correct4
Incorrect-1
In a transformer, number of turns in the primary coil are {tex}140{/tex} and that in the secondary coil are {tex}280{/tex} . If current in primary coil is {tex} 4\mathrm { A } {/tex} , then that in the secondary coil is
{tex} 4\mathrm { A } {/tex}
{tex}2\mathrm A {/tex}
{tex} 6\mathrm { A } {/tex}
{tex} 10\mathrm { A } {/tex}
Correct4
Incorrect-1
Two coils are placed close to each other. The mutual inductance of the pair of coils depends upon
the rates at which currents are changing in the two coils
relative position and orientation of the two coils
the materials of the wires of the coils
the currents in the two coils
Correct4
Incorrect-1
When the current changes from {tex} + 2 \mathrm { A } {/tex} to {tex} - 2 \mathrm { A } {/tex} in {tex} 0.05\, \mathrm{second}{/tex}, an {tex}e.m.f{/tex}. of {tex} 8 \mathrm { V } {/tex} is induced in a coil. The coefficient of self- induction of the coil is
{tex}0.2 \mathrm { H } {/tex}
{tex} 0.4\mathrm { H } {/tex}
{tex} 0.8\ \mathrm { H } {/tex}
{tex}0.1 \mathrm { H } {/tex}
Correct4
Incorrect-1
In an oscillating {tex} LC {/tex} circuit the maximum charge on the capacitor is {tex} Q {/tex} . The charge on the capacitor when the energy is stored equally between the electric and magnetic field is
{tex} \frac { Q } { 2 } {/tex}
{tex} \frac { Q } { \sqrt { 3 } } {/tex}
{tex} \frac { Q } { \sqrt { 2 } } {/tex}
{tex} Q {/tex}
Correct4
Incorrect-1
The core of any transformer is laminated so as to
reduce the energy loss due to eddy currents
make it light weight
make it robust and strong
increase the secondary voltage
Correct4
Incorrect-1
Alternating current can not be measured by D.C. ammeter because
Average value of current for complete cycle is zero
A.C. Changes direction
A.C. can not pass through D.C. Ammeter
D.C. Ammeter will get damaged.
Correct4
Incorrect-1
In an {tex} L C R {/tex} series a.c. circuit, the voltage across each of the components, {tex} L , C {/tex} and {tex} R {/tex} is {tex} \mathrm 50{ V } {/tex} . The voltage across the {tex} L C {/tex} combination will be
{tex}100 \mathrm { V } {/tex}
{tex}50 \sqrt { 2 } \mathrm { V } {/tex}
{tex}50 \mathrm { V } {/tex}
{tex} 0\mathrm { V } ( \text { zero } ) {/tex}
Correct4
Incorrect-1
A coil having n turns and resistance {tex} R \Omega {/tex} is connected with a galvanometer of resistance {tex} 4R \Omega {/tex} . This combination is moved in time {tex} \mathrm t {/tex} seconds from a magnetic field {tex} W _ { 1 } {/tex} weber to {tex} W _ { 2 } {/tex} weber. The induced current in the circuit is
{tex} - \frac { \left( W _ { 2 } - W _ { 1 } \right) } { R n t } {/tex}
{tex} - \frac { n \left( W _ { 2 } - W _ { 1 } \right) } { 5 R t } {/tex}
{tex} - \frac { \left( W _ { 2 } - W _ { 1 } \right) } { 5 R n t } {/tex}
{tex} - \frac { n \left( W _ { 2 } - W _ { 1 } \right) } { R t } {/tex}
Correct4
Incorrect-1
In a uniform magnetic field of induction {tex} B {/tex} a wire in the form of a semicircle of radius {tex}r{/tex} rotates about the diameter of the circle with an angular frequency {tex} \omega {/tex} . The axis of rotation is perpendicular to the field. If the total resistance of the circuit is {tex} R {/tex} , the mean power generated per period of rotation is
{tex} \frac { ( B \pi r \omega ) ^ { 2 } } { 2 R } {/tex}
{tex} \frac { \left( B \pi r ^ { 2 } \omega \right) ^ { 2 } } { 8 R } {/tex}
{tex} \frac { B \pi r ^ { 2 } \omega } { 2 R } {/tex}
{tex} \frac { \left( B \pi r \omega ^ { 2 } \right) ^ { 2 } } { 8 R } {/tex}
Correct4
Incorrect-1
In a {tex} L C R {/tex} circuit capacitance is changed from {tex} C {/tex} to {tex} 2 C . {/tex} For the resonant frequency to remain unchanged, the inductance should be changed from {tex} L {/tex} to
{tex} L/2 {/tex}
{tex}2 L {/tex}
{tex}4 L {/tex}
{tex} L / 4 {/tex}
Correct4
Incorrect-1
A metal conductor of length {tex} 1\mathrm { m } {/tex} rotates vertically about one of its ends at angular velocity {tex} 5 {/tex} radians per second. If the horizontal component of earth's magnetic field is {tex} 0.2 \times 10 ^ { - 4 } \mathrm { T } {/tex} , then the e.m.f. developed between the two ends of the conductor is
{tex} 5\mathrm { mV } {/tex}
{tex}50 \mu \mathrm { V } {/tex}
{tex} 5\mu \mathrm { V } {/tex}
{tex}50 \mathrm { mV } {/tex}
Correct4
Incorrect-1
One conducting {tex} U {/tex} tube can slide inside another as shown in figure, maintaining electrical contacts between the tubes. The magnetic field {tex} B {/tex} is perpendicular to the plane of the figure. If each tube moves towards the other at a constant speed {tex} v , {/tex} then the emf induced in the circuit in terms of {tex} B , l {/tex} and {tex} v {/tex} where {tex} l {/tex} is the width of each tube, will be
{tex} - B l v {/tex}
{tex} B l v {/tex}
{tex}2 B l v {/tex}
zero
Correct4
Incorrect-1
The self inductance of the motor of an electric fan is {tex} 10\mathrm { H. } {/tex} In order to impart maximum power at {tex}50 \mathrm { Hz } {/tex} , it should be connected to a capacitance of
{tex} 8\mu \mathrm { F } {/tex}
{tex}4 \mu \mathrm { F } {/tex}
{tex}2 \mu \mathrm { F } {/tex}
{tex}1 \mu \mathrm { F } {/tex}
Correct4
Incorrect-1
The phase difference between the alternating current and emf is {tex} \frac { \pi } { 2 } . {/tex} Which of the following cannot be the constituent of the circuit?
{tex} R , L {/tex}
{tex} {C} {/tex} alone
{tex} L {/tex} alone
{tex} L , C {/tex}
Correct4
Incorrect-1
A circuit has a resistance of {tex}12\,\mathrm{ohm}{/tex} and an impedance of {tex}15\,\mathrm{ohm}{/tex}. The power factor of the circuit will be
0.4
0.8
0.125
1.25
Correct4
Incorrect-1
A coil of inductance {tex} 300\mathrm { mH } {/tex} and resistance {tex}2 \Omega {/tex} is connected to a source of voltage {tex}2 \mathrm { V } {/tex} . The current reaches half of its steady state value in
{tex} 0.1 \mathrm { s } {/tex}
0.05{tex} \mathrm { s } {/tex}
{tex}0.3 \mathrm { s } {/tex}
{tex} 0.15 \mathrm { s } {/tex}
Correct4
Incorrect-1
Which of the following units denotes the dimension {tex} \frac { \mathrm { ML } ^ { 2 } } { \mathrm { Q } ^ { 2 } } {/tex} where {tex} Q {/tex} denotes the electric charge?
{tex} \mathrm { Wb } / \mathrm { m } ^ { 2 } {/tex}
{tex} \mathrm {Henry(H)} {/tex}
{tex} \mathrm { H/m } ^ { 2 } {/tex}
{tex} \mathrm {Weber (Wb)} {/tex}
Correct4
Incorrect-1
In a series resonant {tex} LCR {/tex} circuit, the voltage across {tex} R {/tex} is {tex}100 \mathrm{volts}{/tex} and {tex} R = 1 \mathrm { k } \Omega {/tex} with {tex} \mathrm { C } = 2 \mu \mathrm { F } {/tex} . The resonant frequency {tex} \omega {/tex} is {tex}200 \mathrm { rad } / \mathrm { s } {/tex} . At resonance the voltage across {tex} L {/tex} is
{tex} 2.5 \times 10 ^ { - 2 } \mathrm { V } {/tex}
{tex}40 \mathrm { V } {/tex}
{tex}250 \mathrm { V } {/tex}
{tex} 4 \times 10 ^ { - 3 } \mathrm { V } {/tex}
Correct4
Incorrect-1
In an {tex} AC {/tex} generator, a coil with {tex} N {/tex} turns, all of the same area {tex} A {/tex} and total resistance {tex} R , {/tex} rotates with frequency {tex} \omega {/tex} in a magnetic field {tex} B {/tex} . The maximum value of emf generated in the coil is
{tex} \mathrm {N.A.B.R. \omega }{/tex}
{tex} \mathrm { N.A.B } {/tex}
{tex} \mathrm {N.A.B.R.} {/tex}
{tex} \mathrm{N.A.B.\omega }{/tex}
Correct4
Incorrect-1
The flux linked with a coil at any instant {tex} ^{ \prime }t ^ { \prime } {/tex} is given by {tex} \phi = 10 t ^ { 2 } - 50 t + 250 {/tex}
The induced emf at {tex} t = 3 s {/tex} is
{tex} - 190 \mathrm { V } {/tex}
{tex} - 10 \mathrm { V } {/tex}
{tex} 10\mathrm { V } {/tex}
{tex} 190 \mathrm { V } {/tex}
Correct4
Incorrect-1
An inductor {tex} ( L = 100 \mathrm { mH } ) , {/tex} a resistor {tex} ( R = 100 \Omega ) {/tex} and a battery {tex} ( E = 100 \mathrm { V } ) {/tex} are initially connected in series as shown in the figure. After a long time the battery is disconnected after short circuiting the points {tex} A {/tex} and {tex} B . {/tex} The current in the circuit {tex}1 \mathrm{ms}{/tex} after the short circuit is
{tex} 1/ \mathrm { eA } {/tex}
{tex} e \mathrm A {/tex}
{tex}0.1 \mathrm { A } {/tex}
{tex}1 \mathrm { A } {/tex}
Correct4
Incorrect-1
In an a.c. circuit the voltage applied is {tex} E = E _ { 0 } \sin \omega t . {/tex} The resulting current in the circuit is {tex} I = I _ { 0 } \sin \left( \omega t - \frac { \pi } { 2 } \right) . {/tex} The power consumption in the circuit is given by
{tex} P = \sqrt { 2 } E _ { 0 } I _ { 0 } {/tex}
{tex} P = \frac { E _ { 0 } I _ { 0 } } { \sqrt { 2 } } {/tex}
{tex} P = \mathrm { zero } {/tex}
{tex} P = \frac { E _ { 0 } I _ { 0 } } { 2 } {/tex}
