# JEE Main > Magnetic Effects of Current and Magnetism

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 popular teachers.

Physics
Chemistry
Maths

Q 1.

Correct4

Incorrect-1

A magnetic needle lying parallel to a magnetic field requires {tex} W {/tex} units of work to turn it through {tex} 60 ^ { \circ } . {/tex} The torque needed to maintain the needle in this position will be

{tex} \sqrt { 3 } W {/tex}

B

{tex} W {/tex}

C

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

D

{tex} 2 W {/tex}

##### Explanation  Q 2.

Correct4

Incorrect-1

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  Q 3.

Correct4

Incorrect-1

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  Q 4.

Correct4

Incorrect-1

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  Q 5.

Correct4

Incorrect-1

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    Q 6.

Correct4

Incorrect-1

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  Q 7.

Correct4

Incorrect-1

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

##### Explanation  Q 8.

Correct4

Incorrect-1

Needles {tex} N _ { 1 } , N _ { 2 } {/tex} and {tex} N _ { 3 } {/tex} are made of a ferromagnetic,
a paramagnetic and a diamagnetic substance respectively. A magnet when brought close to them will

A

attract all three of them

B

attract {tex} N _ { 1 } {/tex} and {tex} N _ { 2 } {/tex} strongly but repel {tex} N _ { 3 } {/tex}

attract {tex} N _ { 1 } {/tex} strongly, {tex} N _ { 2 } {/tex} weakly and repel {tex} N _ { 3 } {/tex} weakly

D

attract {tex} N _ { 1 } {/tex} strongly, but repel {tex} N _ { 2 } {/tex} and {tex} N _ { 3 } {/tex} weakly.

##### Explanation  Q 9.

Correct4

Incorrect-1

Relative permittivity and permeability of a material are {tex} \varepsilon _ { r } {/tex} and {tex} \mu _ { r } , {/tex} respectively. Which of the following values of these quantities are allowed for a diamagnetic mateiral?

A

{tex} \varepsilon _ { r } = 1.5 , \mu _ { r } = 1.5 {/tex}

B

{tex} \varepsilon _ { r } = 0.5 , \mu _ { r } = 1.5 {/tex}

{tex} \varepsilon _ { r } = 1.5 , \mu _ { r } = 0.5 {/tex}

D

{tex} \varepsilon _ { r } = 0.5 , \mu _ { r } = 0.5 {/tex}

##### Explanation  Q 10.

Correct4

Incorrect-1

A length {tex}L{/tex} of wire carries a steady current {tex}i{/tex}. It is bent first to form a circular plane coil of one turn. The same length is now bent more sharply to give a double loop of smaller radius. The magnetic field at the centre caused by the same current is

A

A quarter of its first value

B

Unaltered

Four times of its first value

D

A half of its first value

##### Explanation     Q 11.

Correct4

Incorrect-1

A vertical straight conductor carries a current vertically upwards. A point {tex} P {/tex} lies to the east of it at a small distance and another point {tex} Q {/tex} lies to the west at the same distance.The magnetic field at {tex} P {/tex} is

A

Greater than at {tex} Q {/tex}

Same as at {tex} Q {/tex}

C

Less than at {tex} Q {/tex}

D

Greater or less than at {tex} Q {/tex} depending upon the strength of the current

##### Explanation  Q 12.

Correct4

Incorrect-1

If a copper rod carries a direct current, the magnetic field associated with the current will be

A

Only inside the rod

B

Only outside the rod

Both inside and outside the rod

D

Neither inside nor outside the rod

##### Explanation Q 13.

Correct4

Incorrect-1

If a long hollow copper pipe carries a direct current, the magnetic field associated with the current will be

A

Only inside the pipe

Only outside the pipe

C

Neither inside nor outside the pipe

D

Both inside and outside the pipe

##### Explanation Q 14.

Correct4

Incorrect-1

The magnetic field {tex} d \vec { B } {/tex} due to a small current element {tex} d l {/tex} at a distance {tex} \vec { r } {/tex} and element carrying current {tex} i {/tex} is, Vector form of Biot-savart's law is

A

{tex} d \vec { B } = \frac { \mu _ { 0 } } { 4 \pi } i \left( \frac { d \vec { l } \times \vec { r } } { r } \right) {/tex}

B

{tex} d \vec { B } = \frac { \mu _ { 0 } } { 4 \pi } i ^ { 2 } \left( \frac { d \vec { l } \times \vec { r } } { r } \right) {/tex}

C

{tex} d \vec { B } = \frac { \mu _ { 0 } } { 4 \pi } i ^ { 2 } \left( \frac { d \vec { l } \times \vec { r } } { r ^ { 2 } } \right) {/tex}

{tex} d \vec { B } = \frac { \mu _ { 0 } } { 4 \pi } i \left( \frac { d \vec { l } \times \vec { r } } { r ^ { 3 } } \right) {/tex}

##### Explanation Q 15.

Correct4

Incorrect-1

A charge {tex} q {/tex} coulomb moves in a circle at {tex} n {/tex} revolutions per second and the radius of the circle is {tex} r {/tex} metre. Then magnetic field at the centre of the circle is

A

{tex} \frac { 2 \pi q } { n r } \times 10 ^ { - 7 } N|amp/metre {/tex}

B

{tex} \frac { 2 \pi q } { r } \times 10 ^ { - 7 } N|amp/metre{/tex}

{tex} \frac { 2 \pi n q } { r } \times 10 ^ { - 7 } N|amp/metre{/tex}

D

{tex} \frac { 2 \pi q } { r } {/tex} N|amp/metre{/tex}

##### Explanation Q 16.

Correct4

Incorrect-1

An infinitely long straight conductor is bent into the shape as shown in the figure. It carries a current of {tex} i {/tex} ampere and the radius of the circular loop is {tex} r {/tex} metre. Then the magnetic induction at its centre will be A

{tex} \frac { \mu _ { 0 } } { 4 \pi } \frac { 2 i } { r } ( \pi + 1 ) {/tex}

{tex} \frac { \mu _ { 0 } } { 4 \pi } \frac { 2 i } { r } ( \pi - 1 ) {/tex}

C

Zero

D

Infinite

##### Explanation   Q 17.

Correct4

Incorrect-1

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   Q 18.

Correct4

Incorrect-1

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   Q 19.

Correct4

Incorrect-1

A straight section {tex} P Q {/tex} of a circuit lies along the {tex} X {/tex} axis from {tex} x = - \frac { a } { 2 } {/tex} to {tex} x = \frac { a } { 2 } {/tex} and carries a steady current {tex} i {/tex}. The magnetic field due to the section {tex} P Q {/tex} at a point {tex} X = + a {/tex} will be

A

Proportional to {tex} a {/tex}

B

Proportional to {tex} a ^ { 2 } {/tex}

C

Proportional to {tex} 1 / a {/tex}

Zero

##### Explanation Q 20.

Correct4

Incorrect-1

A helium nucleus makes a full rotation in a circle of radius {tex} 0.8 \ metre {/tex} in two seconds. The value of the magnetic field {tex} B {/tex} at the centre of the circle will be

A

{tex} \frac { 10 ^ { - 19 } } { \mu _ { 0 } } {/tex}

{tex} 10 ^ { - 19 } \mu _ { 0 } {/tex}

C

{tex} 2 \times 10 ^ { - 10 } \mu _ { 0 } {/tex}

D

{tex} \frac { 2 \times 10 ^ { - 10 } } { \mu _ { 0 } } {/tex}

##### Explanation Q 21.

Correct4

Incorrect-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 } \mathrm { Tesla } {/tex}

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 Q 22.

Correct4

Incorrect-1

The magnetic induction at a point {tex} P {/tex} which is distant {tex} 4\ cm {/tex} from a long current carrying wire is {tex} 10 ^ { - 8 } {/tex} Tesla. The field of induction at a distance {tex} 12 \ cm {/tex} from the same current would be

{tex} 3.33 \times 10 ^ { - 9 } {/tex} Tesla

B

{tex} 1.11 \times 10 ^ { - 4 } {/tex} Tesla

C

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

D

{tex} 9 \times 10 ^ { - 2 } {/tex} Tesla

##### Explanation Q 23.

Correct4

Incorrect-1

The strength of the magnetic field at a point {tex} r {/tex} near a long straight current carrying wire is {tex} B {/tex}. The field at a distance {tex} \frac { r } { 2 } {/tex} will be

A

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

B

{tex} \frac { B } { 4 } {/tex}

{tex} 2\ B {/tex}

D

{tex} 4 \ B {/tex}

##### Explanation Q 24.

Correct4

Incorrect-1

Field at the centre of a circular coil of radius {tex} r {/tex}, through which a current {tex} I {/tex} flows is

A

Directly proportional to {tex} r {/tex}

B

Inversely proportional to {tex} I {/tex}

Directly proportional to {tex} I {/tex}

D

Directly proportional to {tex} I ^ { 2 } {/tex}

##### Explanation Q 25.

Correct4

Incorrect-1

A current of {tex} 0.1\ A {/tex} circulates around a coil of {tex}100 {/tex} turns and having a radius equal to {tex} 5 \ cm . {/tex} The magnetic field set up at the centre of the coil is {tex} ({\mu _ { 0 } = 4 \pi \times 10 ^ { - 7 }} {/tex} {tex}weber / ampere - metre){/tex}

{tex} 4 \pi \times 10 ^ { - 5 } {/tex} tesla

B

{tex} 8 \pi \times 10 ^ { - 5 } {/tex} tesla

C

{tex} 4 \times 10 ^ { - 5 } {/tex} tesla

D

{tex} 2 \times 10 ^ { - 5 } {/tex} tesla

##### Explanation 