# JEE Main

Explore popular questions from Magnetic Effects of Current and Magnetism for JEE Main. This collection covers Magnetic Effects of Current and Magnetism previous year JEE Main questions hand picked by experienced teachers.

## Mathematics

Magnetic Effects of Current and Magnetism

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Q 1. A solenoid of {tex} 1.5 \ metre {/tex} length and {tex} 4.0 \ cm {/tex} diameter posses {tex}10{/tex} turn per {tex} c m . {/tex} A current of {tex}5\ ampere{/tex} is flowing through it. The magnetic induction at axis inside the solenoid is

{tex} 2 \pi \times 10 ^ { - 3 } {/tex} Tesla

B

{tex} 2 \pi \times 10 ^ { - 5 } {/tex} Tesla

C

{tex} 4 \pi \times 10 ^ { - 2 } {/tex} Gauss

D

{tex} 2 \pi \times 10 ^ { - 5 } {/tex} Gauss

##### Explanation

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Q 2. The line on earth's surface joining the points where the earth's magnetic field is horizontal is called

A

Magnetic meridian

B

Magnetic axis

C

Magnetic line

Magnetic equator

##### Explanation

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Q 3. The magnetic induction field at the centre {tex} C {/tex} of the arrangement shown in Fig. 15.38 is

{tex} \frac { \mu _ { 0 } I} { 4 \pi r } ( 1 + \pi ) {/tex}

B

{tex} \frac { \mu _ { 0 } I} { 2 \pi r } ( 1 + \pi ) {/tex}

C

{tex} \frac { \mu _ { 0 } I } { \pi r } ( 1 + \pi ) {/tex}

D

{tex} \frac { \mu _ { 0 } I } { r } ( 1 + \pi ) {/tex}

##### Explanation

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Q 4. Curie temperature is the temperature above which

A

a paramagnetic material becomes diamagnetic.

B

a ferromagnetic material becomes diamagnetic.

C

a paramagnetic material becomes ferromagnetic.

a ferromagnetic material becomes paramagnetic.

##### Explanation

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Q 5. A charged particle moves in a uniform magnetic field of induction {tex}\overrightarrow{B}{/tex} with a velocity {tex}\overrightarrow{v}{/tex}. The change in kinetic energy in the magnetic field is zero when the velocity {tex}\overrightarrow{v}{/tex} is

A

parallel to {tex} \vec { B } {/tex}

B

perpendicular to {tex} \vec { B } {/tex}

at any angle to {tex} \vec { B } {/tex}

D

None of these

##### Explanation

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Q 6. An equilateral triangular current loop {tex} P Q R {/tex} carries a current I ampere. Length of each side is {tex} l {/tex} metre. A uniform magnetic field of induction {tex} \vec { B } {/tex} exists in a direction parallel to {tex} P Q {/tex} . Then the force on the side {tex} P Q {/tex} is

A

{tex} I l B {/tex}

B

{tex} \frac { I l B } { 2 } {/tex}

C

{tex} \left( \frac { I l B } { 2 } \right) \sqrt { 3 } {/tex}

Zero

##### Explanation

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Q 7. Two long thin wires {tex} A B C {/tex} and {tex} D E F {/tex} are arranged as shown. They carry current {tex} I {/tex} as shown. The magnitude of the magnetic field at {tex} O {/tex} is

A

Zero

B

{tex} \frac { \mu _ { 0 } I } { 4 \pi a } {/tex}

{tex} \frac { \mu _ { 0 } I } { 2 \pi a } {/tex}

D

{tex} \frac { \mu _ { 0 } I } { 2 \sqrt { 2 } \pi a } {/tex}

##### Explanation

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Q 8. A magnetic needle is kept in a non-uniform magnetic field. It experiences

A

A torque but not a force.

B

Neither a force nor a torque.

A force and a torque.

D

A force but not a torque.

##### Explanation

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Q 9. A charged particle moves with velocity {tex} \vec { v } {/tex} in a uniform magnetic field {tex} \vec { B } . {/tex} The magnetic force experienced by the particle is

A

always zero.

B

never zero.

C

zero if {tex} \vec { B } {/tex} and {tex} \vec { v } {/tex} are perpendicular.

zero if {tex} \vec { B } {/tex} and {tex} \vec { v } {/tex} are parallel.

##### Explanation

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Q 10. A particle of charge {tex} - 16 \times 10 ^ { - 18 } {/tex} C moving with velocity {tex} 10 \mathrm { m } / \mathrm { s } {/tex} along the {tex} x {/tex} -axis enters a region where a magnetic field of induction {tex} B {/tex} is along the {tex} y {/tex} -axis and an electric field of magnitude {tex} 10 ^ { 4 } \mathrm { V } / \mathrm { m } {/tex} is along the negative {tex} z {/tex} -axis. If the charged particle continues moving along the {tex} x {/tex} -axis, the magnitude of {tex} B {/tex} is

{tex} 10 ^ { 3 } \mathrm { Wb } / \mathrm { m } ^ { 2 } {/tex}

B

{tex} 10 ^ { 5 } \mathrm { Wb } / \mathrm { m } ^ { 2 } {/tex}

C

{tex} 10 ^ { 16 } \mathrm { Wb } / \mathrm { m } ^ { 2 } {/tex}

D

{tex} 10 ^ { - 3 } \mathrm { Wb } / \mathrm { m } ^ { 2 } {/tex}

##### Explanation

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Q 11. Two concentric coils each of radius equal to 2{tex} \pi \mathrm { cm } {/tex} are placed at right angles to each other, 3{tex} \mathrm { A } {/tex} and 4{tex} \mathrm { A } {/tex} are the currents flowing in coils, respectively. The magnetic induction in {tex} \mathrm { Wb } / \mathrm { m } ^ { 2 } {/tex} at the centre of the coils will be {tex} \left( \mu _ { 0 } = 4 \pi \times 10 ^ { - 7 } \mathrm { Wb } / \mathrm { Am } \right) {/tex}

A

{tex} 12 \times 10 ^ { - 5 } {/tex}

B

{tex} 10 ^ { - 5 } {/tex}

{tex} 5 \times 10 ^ { - 5 } {/tex}

D

{tex} 7 \times 10 ^ { - 5 } {/tex}

##### Explanation

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Q 12. An equilateral triangular loop {tex} A C D {/tex} of side length {tex} l {/tex} carries a current {tex} i {/tex} in the direction shown in Fig. {tex} 15.41 . {/tex} The loop is kept in a uniform horizontal magnetic field {tex} \vec { B } {/tex} as shown in Fig. 15.41 , net force on the loop is

Zero

B

{tex} \frac { \sqrt { 3 } } { 2 } i B {/tex}

C

Perpendicular to paper inwards.

D

Perpendicular to paper outwards.

##### Explanation

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Q 13. Two particles {tex} X {/tex} and {tex} Y {/tex} having equal charges, after being accelerated through the same potential difference, enter a region of uniform magnetic field and and and and and and and and and and describe circular paths of radii {tex} R _ { 1 } {/tex} and {tex} R _ { 2 } {/tex} , respectively. The ratio of masses of {tex} X {/tex} and {tex} Y {/tex} is

A

{tex} \left( \frac { R _ { 1 } } { R _ { 2 } } \right) ^ { 1 / 2 } {/tex}

B

{tex} \frac { R _ { 2 } } { R _ { 1 } } {/tex}

{tex} \left( \frac { R _ { 1 } } { R _ { 2 } } \right) ^ { 2 } {/tex}

D

{tex} \left( \frac { R _ { 1 } } { R _ { 2 } } \right) {/tex}

##### Explanation

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Q 14. A current-carrying conductor is looped into a circle of radius {tex} 10 \mathrm { cm } . {/tex} The magnetic moment of the current loop becomes {tex} 0.314 \mathrm { A } / \mathrm { m } ^ { 2 } . {/tex} What is the current in the loop?

A

{tex}5 \mathrm { A } {/tex}

B

{tex}8 \mathrm A{/tex}

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

D

{tex}12 \mathrm { A } {/tex}

##### Explanation

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Q 15. Two straight long conductors {tex} A O B {/tex} and {tex} C O D {/tex} are per- pendicular to each other and carry currents {tex} i _ { 1 } {/tex} and {tex} i _ { 2 } {/tex} . The magnitude of the magnetic induction at a point {tex} P {/tex} at a distance {tex} a {/tex} from the point {tex} O {/tex} in a direction perpen- dicular to the plane {tex} A C B D {/tex} is

A

{tex} \frac { \mu _ { 0 } } { 2 \pi a } \left( i _ { 1 } + i _ { 2 } \right) {/tex}

B

{tex} \frac { \mu _ { 0 } } { 2 \pi a } \left( i _ { 1 } - i _ { 2 } \right) {/tex}

{tex} \frac { \mu _ { 0 } } { 2 \pi a } \left( i _ { 1 } ^ { 2 } + i _ { 2 } ^ { 2 } \right) ^ { 1 / 2 } {/tex}

D

{tex} \frac { \mu _ { 0 } } { 2 \pi a } \frac { i _ { 1 } i _ { 2 } } { \left( i _ { 1 } + i _ { 2 } \right) } {/tex}

##### Explanation

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Q 16. Shown in Fig. 15.45 is a conductor carrying a current I. The magnetic field intensity at the point {tex} O {/tex} (common centre of all the three arcs) is {tex} ( \theta \text { in radian) } {/tex}

{tex} \frac { 5 \mu _ { 0 } I \theta } { 24 \pi r } {/tex}

B

{tex} \frac { \mu _ { 0 } I \theta } { 24 \pi r } {/tex}

C

{tex} \frac { 11 \mu _ { 0 } I \theta } { 24 \pi r } {/tex}

D

Zero

##### Explanation

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Q 17. A particle of mass {tex} m {/tex} and charge {tex} q {/tex} is projected from origin with initial velocity {tex} [ u \hat { i } - v\hat{j}]{/tex}. Uniform electric and magnetic field exist in the region along {tex} + y {/tex} direction of magnitudes {tex} E {/tex} and {tex} B {/tex} , respectively. Then particle will definitively return to the origin if

A

{tex} \frac { v B } { 2 \pi E } {/tex} is an integer

B

{tex} \frac { \left( u ^ { 2 } + v ^ { 2 } \right) ^ { 1 / 2 } } { [ B / \pi E ] } {/tex} is an integer

{tex} \frac { v B } { \pi E } {/tex} is an integer

D

{tex} \frac { v B } { 3 \pi E } {/tex} is an integer

##### Explanation

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Q 18. The materials suitable for making electromagnets should have

A

High retentivity and high coercivity

Low retentivity and low coercivity

C

High retentivity and low coercivity

D

Low retentivity and high coercivity.

##### Explanation

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Q 19. A thin rectangular magnet suspended freely has a period of oscillation equal to {tex} T . {/tex} Now it is broken into two equal halves (each having half of the original length) and one piece is made to oscillate freely in the same field. If its period of oscillation is {tex} T ^ { \prime } , {/tex} the ratio {tex} \frac { T ^ { \prime } } { T } {/tex} is

A

{tex} \frac { 1 } { 2 \sqrt { 2 } } {/tex}

{tex} \frac { 1 } { 2 } {/tex}

C

{tex}2{/tex}

D

{tex} \frac { 1 } { 4 } {/tex}

##### Explanation

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Q 20. A current {tex} i {/tex} ampere flows in a circular arc of wire whose radius is {tex} R , {/tex} which subtend an angle {tex} 3 \pi / 2 {/tex} radian at its centre. The magnetic induction {tex} B {/tex} at the centre is

A

{tex} \frac { \mu _ { 0 } i } { R } {/tex}

B

{tex} \frac { \mu _ { 0 } i } { 2 R } {/tex}

C

{tex} \frac { 2 \mu _ { 0 } i } { R } {/tex}

{tex} \frac { 3 \mu _ { 0 } i } { 8 R } {/tex}

##### Explanation

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Q 21. The magnetic lines of force inside a bar magnet

A

Are from north-pole to south-pole of the magnet

B

Do not exist

C

Depend upon the area of cross-section of the bar magnet

Are from south-pole to north-pole of the magnet.

##### Explanation

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Q 22. A current {tex} i {/tex} ampere flows along the inner conductor of a coaxial cable and returns along the outer conductor of the cable, then the magnetic induction at any point outside the conductor at a distance {tex} r {/tex} metre from the axis is

A

{tex} \infty {/tex}

{tex} Zero {/tex}

C

{tex} \frac { \mu _ { 0 } } { 4 \pi } \frac { 2 i } { r } {/tex}

D

{tex} \frac { \mu _ { 0 } } { 4 \pi } \frac { 2 \pi i } { r } {/tex}

##### Explanation

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Q 23. Curie temperature is the temperature above which

A ferromagnetic material becomes paramagnetic

B

A paramagnetic material becomes diamagnetic

C

A ferromagnetic material becomes diamagnetic

D

A paramagnetic material becomes ferromagnetic.

##### Explanation

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Q 24. The length of a magnet is large compared to its width and breadth. The time period of its oscillation in a vibration magnetometer is {tex} 2\mathrm {\ s}{/tex}. The magnet is cut along its length into three equal parts and three parts are then placed on each other with their like poles together. The time period of this combination will be

A

{tex} 2 \mathrm {\ s } {/tex}

{tex} \frac { 2 } { 3 } s {/tex}

C

{tex} ( 2 \sqrt { 3 } ) s {/tex}

D

{tex} \left( \frac { 2 } { \sqrt { 3 } } \right) s {/tex}

##### Explanation

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Q 25. A magnetic needle is kept in a non-uniform magnetic field. It experiences

a force and a torque

B

a force but not a torque

C

a torque but not a force

D

neither a force nor a torque