JEE Main > Electromagnetic Induction and Alternating Currents

Explore popular questions from Electromagnetic Induction and Alternating Currents for JEE Main. This collection covers Electromagnetic Induction and Alternating Currents previous year JEE Main questions hand picked by popular teachers.


Q 1.    

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

A

{tex} R / \omega L {/tex}

{tex} R / \left( R ^ { 2 } + \omega ^ { 2 } L ^ { 2 } \right) ^ { 1 / 2 } {/tex}

C

{tex} \omega L / R {/tex}

D

{tex} R / \left( R ^ { 2 } - \omega ^ { 2 } L ^ { 2 } \right) ^ { 1 / 2 } {/tex}

Explanation





Q 2.    

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

A

{tex} zero{/tex}

B

{tex} R v B {/tex}

C

{tex} v B L / R {/tex}

{tex} v B I {/tex}

Explanation





Q 3.    

Correct4

Incorrect-1

The inductance between {tex} A {/tex} and {tex} D {/tex} is

A

{tex} 3.66\ \mathrm { H } {/tex}

B

{tex} 9\mathrm { H } {/tex}

C

{tex} 0.66\mathrm { H } {/tex}

{tex} 1 \mathrm { H } {/tex}

Explanation





Q 4.    

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

A

{tex} 4\mathrm { A } {/tex}

{tex}2\mathrm A {/tex}

C

{tex} 6\mathrm { A } {/tex}

D

{tex} 10\mathrm { A } {/tex}

Explanation





Q 5.    

Correct4

Incorrect-1

Two coils are placed close to each other. The mutual inductance of the pair of coils depends upon

A

the rates at which currents are changing in the two coils

relative position and orientation of the two coils

C

the materials of the wires of the coils

D

the currents in the two coils

Explanation

Q 6.    

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

A

{tex}0.2 \mathrm { H } {/tex}

B

{tex} 0.4\mathrm { H } {/tex}

C

{tex} 0.8\ \mathrm { H } {/tex}

{tex}0.1 \mathrm { H } {/tex}

Explanation





Q 7.    

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

A

{tex} \frac { Q } { 2 } {/tex}

B

{tex} \frac { Q } { \sqrt { 3 } } {/tex}

{tex} \frac { Q } { \sqrt { 2 } } {/tex}

D

{tex} Q {/tex}

Explanation





Q 8.    

Correct4

Incorrect-1

The core of any transformer is laminated so as to

reduce the energy loss due to eddy currents

B

make it light weight

C

make it robust and strong

D

increase the secondary voltage

Explanation

Q 9.    

Correct4

Incorrect-1

Alternating current can not be measured by D.C. ammeter because

Average value of current for complete cycle is zero

B

A.C. Changes direction

C

A.C. can not pass through D.C. Ammeter

D

D.C. Ammeter will get damaged.

Explanation

Q 10.    

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

A

{tex}100 \mathrm { V } {/tex}

B

{tex}50 \sqrt { 2 } \mathrm { V } {/tex}

C

{tex}50 \mathrm { V } {/tex}

{tex} 0\mathrm { V } ( \text { zero } ) {/tex}

Explanation

Q 11.    

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

A

{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}

C

{tex} - \frac { \left( W _ { 2 } - W _ { 1 } \right) } { 5 R n t } {/tex}

D

{tex} - \frac { n \left( W _ { 2 } - W _ { 1 } \right) } { R t } {/tex}

Explanation







Q 12.    

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

A

{tex} \frac { ( B \pi r \omega ) ^ { 2 } } { 2 R } {/tex}

{tex} \frac { \left( B \pi r ^ { 2 } \omega \right) ^ { 2 } } { 8 R } {/tex}

C

{tex} \frac { B \pi r ^ { 2 } \omega } { 2 R } {/tex}

D

{tex} \frac { \left( B \pi r \omega ^ { 2 } \right) ^ { 2 } } { 8 R } {/tex}

Explanation





Q 13.    

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}

B

{tex}2 L {/tex}

C

{tex}4 L {/tex}

D

{tex} L / 4 {/tex}

Explanation


Q 14.    

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

A

{tex} 5\mathrm { mV } {/tex}

{tex}50 \mu \mathrm { V } {/tex}

C

{tex} 5\mu \mathrm { V } {/tex}

D

{tex}50 \mathrm { mV } {/tex}

Explanation



Q 15.    

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

A

{tex} - B l v {/tex}

B

{tex} B l v {/tex}

{tex}2 B l v {/tex}

D

zero

Explanation

Q 16.    

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

A

{tex} 8\mu \mathrm { F } {/tex}

B

{tex}4 \mu \mathrm { F } {/tex}

C

{tex}2 \mu \mathrm { F } {/tex}

{tex}1 \mu \mathrm { F } {/tex}

Explanation



Q 17.    

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}

B

{tex} {C} {/tex} alone

C

{tex} L {/tex} alone

D

{tex} L , C {/tex}

Explanation

Q 18.    

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

A

0.4

0.8

C

0.125

D

1.25

Explanation

Q 19.    

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}

B

0.05{tex} \mathrm { s } {/tex}

C

{tex}0.3 \mathrm { s } {/tex}

D

{tex} 0.15 \mathrm { s } {/tex}

Explanation





Q 20.    

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?

A

{tex} \mathrm { Wb } / \mathrm { m } ^ { 2 } {/tex}

{tex} \mathrm {Henry(H)} {/tex}

C

{tex} \mathrm { H/m } ^ { 2 } {/tex}

D

{tex} \mathrm {Weber (Wb)} {/tex}

Explanation


Q 21.    

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

A

{tex} 2.5 \times 10 ^ { - 2 } \mathrm { V } {/tex}

B

{tex}40 \mathrm { V } {/tex}

{tex}250 \mathrm { V } {/tex}

D

{tex} 4 \times 10 ^ { - 3 } \mathrm { V } {/tex}

Explanation





Q 22.    

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

A

{tex} \mathrm {N.A.B.R. \omega }{/tex}

B

{tex} \mathrm { N.A.B } {/tex}

C

{tex} \mathrm {N.A.B.R.} {/tex}

{tex} \mathrm{N.A.B.\omega }{/tex}

Explanation





Q 23.    

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

A

{tex} - 190 \mathrm { V } {/tex}

{tex} - 10 \mathrm { V } {/tex}

C

{tex} 10\mathrm { V } {/tex}

D

{tex} 190 \mathrm { V } {/tex}

Explanation



Q 24.    

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}

B

{tex} e \mathrm A {/tex}

C

{tex}0.1 \mathrm { A } {/tex}

D

{tex}1 \mathrm { A } {/tex}

Explanation









Q 25.    

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

A

{tex} P = \sqrt { 2 } E _ { 0 } I _ { 0 } {/tex}

B

{tex} P = \frac { E _ { 0 } I _ { 0 } } { \sqrt { 2 } } {/tex}

{tex} P = \mathrm { zero } {/tex}

D

{tex} P = \frac { E _ { 0 } I _ { 0 } } { 2 } {/tex}

Explanation