# NEET > Magnetic Effects of Current and Magnetism

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

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Q 1.

Correct4

Incorrect-1

An insulating rod of length {tex} \ell {/tex} carries a charge {tex} q {/tex} distributed uniformly on it. The rod is pivoted at its mid point and is rotated at a frequency fabout a fixed axis perpendicular to rod and passing through the pivot. The magnetic moment of the rod system is {tex} \frac { 1 } { 2 a } \pi q f \ell ^ { 2 } . {/tex} Find the value of a.

6

B

4

C

5

D

8

##### Explanation Q 2.

Correct4

Incorrect-1 A

zero

B

infinite

C

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

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

##### Explanation Q 3.

Correct4

Incorrect-1

A closely wound solenoid of 2000 turns and area of cross- section {tex} 1.5 \times 10 ^ { - 4 } \mathrm { m } ^ { 2 } {/tex} carries a current of 2.0{tex} \mathrm { A } {/tex} . It suspended through its centre and perpendicular to its length, allowing it to turn in a horizontal plane in a uniform magnetic field
{tex} 5 \times 10 ^ { - 2 } {/tex} tesla making an angle of {tex} 30 ^ { \circ } {/tex} with the axis of the solenoid. The torque on the solenoid will be:

A

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

B

{tex} 3 \times 10 ^ { - 3 } \mathrm { N } - \mathrm { m } {/tex}

C

{tex} 1.5 \times 10 ^ { - 3 } \mathrm { N } - \mathrm { m } {/tex}

{tex} 1.5 \times 10 ^ { - 2 } \mathrm { N } - \mathrm { m } {/tex}

##### Explanation Q 4.

Correct4

Incorrect-1

An alternating electric field, of frequency {tex} v , {/tex} is applied across {tex} \text { the dees (radius } = R ) {/tex} of a cyclotron that is being used to {tex} \text { accelerate protons (mass } = m ) . {/tex} The operating magnetic field (B) used in the cyclotron and the kinetic energy {tex} ( K ) {/tex} of the proton beam, produced by it, are given by:

A

{tex} B = \frac { m v } { e } {/tex} and {tex} K = 2 m \pi ^ { 2 } v ^ { 2 } R ^ { 2 } {/tex}

B

{tex} B = \frac { 2 \pi m v } { e } {/tex} and {tex} K = m ^ { 2 } \pi v R ^ { 2 } {/tex}

{tex} B = \frac { 2 \pi m v } { e } {/tex} and {tex} K = 2 m \pi ^ { 2 } v ^ { 2 } R ^ { 2 } {/tex}

D

{tex} B = \frac { m v } { e } {/tex} and {tex} K = m ^ { 2 } \pi v R ^ { 2 } {/tex}

##### Explanation Q 5.

Correct4

Incorrect-1

A galvanometer of 50 ohm resistance has 25 divisions. A current of {tex} 4 \times 10 ^ { - 4 } {/tex} ampere gives a deflection of one per division. To convert this galvanometer into a voltmeter having a range of 25 volts, it should be connected with a resistance of

2450{tex} \Omega {/tex} in series

B

2500{tex} \Omega {/tex} in series.

C

245{tex} \Omega {/tex} in series.

D

2550{tex} \Omega {/tex} in series.

##### Explanation Q 6.

Correct4

Incorrect-1

If we double the radius of a coil keeping the current through it unchanged, then the magnetic field at anypoint at a large distance from the centre becomes approximately

A

double

B

three times

four times

D

one-fourth

##### Explanation Q 7.

Correct4

Incorrect-1

A particle of mass {tex} \mathrm { m } , {/tex} charge {tex} \mathrm { Q } {/tex} and kinetic energy T enters a transverse uniform magnetic field of induction {tex} \overrightarrow { \mathrm { B } } {/tex} . After 3 seconds, the kinetic energy of the particle will be:

A

3T

B

2T

{tex} T {/tex}

D

4T

##### Explanation Q 8.

Correct4

Incorrect-1

A 10 eV electron is circulating in a plane at right angles to a uniform field at magnetic induction {tex} 10 ^ { - 4 } \mathrm { Wb } / \mathrm { m } ^ { 2 } ( = 1.0 {/tex} gauss). The orbital radius of the electron is

A

12cm

B

16{tex} \mathrm { cm } {/tex}

11{tex} \mathrm { cm } {/tex}

D

18{tex} \mathrm { cm } {/tex}

##### Explanation Q 9.

Correct4

Incorrect-1

A uniform electric field and a uniform magnetic field exist in a region in the same direction. An electron is projected with velocity pointed in the same direction. The electron will

A

turn to its right

B

turn to its left

C

keep moving in the same direction but its speed will increase

keep moving in the same direction but its speed will decrease

##### Explanation Q 10.

Correct4

Incorrect-1

Proton, deuteron and alpha particle of same kinetic energy are moving in circular trajectories in a constant magnetic field. The radii of proton, deuteron and alpha particle are respectively {tex} r _ { p } , r _ { d } {/tex} and {tex} r _ { \alpha } {/tex} . Which one of the following relation is correct?

A

{tex} r _ { \alpha } = r _ { p } = r _ { d } {/tex}

{tex} r _ { \alpha } = r _ { p } < r _ { d } {/tex}

C

{tex} r _ { \alpha } > r _ { d } > r _ { p } {/tex}

D

{tex} r _ { \alpha } = r _ { d } > r _ { p } {/tex}

##### Explanation Q 11.

Correct4

Incorrect-1

A moving coil galvanometer has 150 equal divisions. Its current sensitivity is 10 -divisions per milliampere and voltage sensitivity is 2 divisions per millivolt. In order that each division reads 1 volt, the resistance in ohms needed to be connected in series with the coil will be

A

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

B

{tex} 10 ^ { 3 } {/tex}

9995

D

99995

##### Explanation  Q 12.

Correct4

Incorrect-1

A 2{tex} \mu \mathrm { C } {/tex} charge moving around a circle with a frequency of {tex} 6.25 \times 10 ^ { 12 } {/tex} Hz produces a magnetic field 6.28 tesla at the centre of the circle. The radius of the circle is

A

2.25{tex} \mathrm { m } {/tex}

B

0.25{tex} \mathrm { m } {/tex}

C

13.0m

1.25{tex} \mathrm { m } {/tex}

##### Explanation Q 13.

Correct4

Incorrect-1

A charged particle with charge {tex} q {/tex} enters a region of constant, uniform and mutually orthogonal fields {tex}\vec E {/tex} and {tex} \vec { B } {/tex} with a velocity {tex} \vec { v } {/tex} perpendicular to both {tex} \vec { E } {/tex} and {tex} \vec { B } {/tex} , and comes out without any change in magnitude or direction of {tex} \vec { v } . {/tex} Then

A

{tex} \vec { v } = \vec { B } \times \vec { E } / E ^ { 2 } {/tex}

{tex} \vec { v } = \vec { E } \times \vec { B } / B ^ { 2 } {/tex}

C

{tex} \vec { v } = \vec { B } \times \vec { E } / B ^ { 2 } {/tex}

D

{tex} \vec { v } = \vec { E } \times \vec { B } / E ^ { 2 } {/tex}

##### Explanation Q 14.

Correct4

Incorrect-1

A square current carrying loop is suspended in a uniform magnetic field acting in the plane of the loop. If the force on one arm of the loop is {tex} \vec { F } {/tex} , the net force on the remaining three arms of the loop is

A

3{tex} \vec { F } {/tex}

{tex} - \vec { F } {/tex}

C

{tex} - 3 \vec { F } {/tex}

D

{tex} \vec { F } {/tex}

##### Explanation Q 15.

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 1{tex} / a {/tex}

Zero

##### Explanation Q 16.

Correct4

Incorrect-1

{tex} A {/tex} and {tex} B {/tex} are {tex} t {/tex} wo conductors carrying a current {tex} i {/tex} in the same direction. {tex} x {/tex} and {tex} y {/tex} are two electron beams moving in the same direction. Then A

there will berepulsion betwen {tex} A {/tex} and {tex} B , {/tex} attraction between {tex} x {/tex} and {tex} y {/tex}

there will be attraction between {tex} A {/tex} and {tex} B , {/tex} repulsion between {tex} x {/tex} and {tex} y {/tex}

C

there will be repulsion between {tex} A {/tex} and {tex} B {/tex} and also {tex} x {/tex} and {tex} y {/tex}

D

there will be attraction between {tex} A {/tex} and {tex} B {/tex} and also {tex} x {/tex} and {tex} y {/tex}

##### Explanation Q 17.

Correct4

Incorrect-1

A galvanometer of resistance, G is shunted by a resistance S ohm. To keep the main current in the circuit unchanged, the resistance to be put in series with the galvanometer is

A

{tex} \frac { \mathrm { S } ^ { 2 } } { ( \mathrm { S } + \mathrm { G } ) } {/tex}

B

{tex} \frac { \mathrm { SG } } { ( \mathrm { S } + \mathrm { G } ) } {/tex}

{tex} \frac { \mathrm { G } ^ { 2 } } { ( \mathrm { S } + \mathrm { G } ) } {/tex}

D

{tex} \frac { G } { ( S + G ) } {/tex}

##### Explanation  Q 18.

Correct4

Incorrect-1

A current {tex} I {/tex} flows in an infinitely long wire with cross section in the form of a semi-circular ring of radius {tex} R {/tex} . The magnitude of the magnetic induction along its axis is:

A

{tex}\frac{\mu_{0} I}{2\pi^{2}R}{/tex}

B

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

C

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

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

##### Explanation Q 19.

Correct4

Incorrect-1

Two equal electric currents are flowing perpendicular to each other as shown in the figure. AB and CD are perpendicular to each other and symmetrically placed with respect to the current flow. Where do we expect to the resultant magnetic field to be zero? On AB

B

On CD

C

On both AB and CD

D

On both OD and BO

##### Explanation Q 20.

Correct4

Incorrect-1

A closed loop PQRS carrying a current is placed in a uniform magnetic field.
If the magnetic forces on segments PS, {tex} \mathrm { SR } , {/tex} and {tex} \mathrm { RQ } {/tex} are {tex} \mathrm { F } _ { 1 } , \mathrm { F } _ { 2 } {/tex} and {tex} \mathrm { F } _ { 3 } {/tex} respectively and are in the plane of the paper and along the directions shown, the force on the segment {tex} \mathrm { QP } {/tex} is

A

{tex} \mathrm { F } _ { 3 } - \mathrm { F } _ { 1 } - \mathrm { F } _ { 2 } {/tex}

{tex} \sqrt { \left( \mathrm { F } _ { 3 } - \mathrm { F } _ { 1 } \right) ^ { 2 } + \mathrm { F } _ { 2 } ^ { 2 } } {/tex}

C

{tex} \sqrt { \left( \mathrm { F } _ { 3 } - \mathrm { F } _ { 1 } \right) ^ { 2 } - \mathrm { F } _ { 2 } ^ { 2 } } {/tex}

D

{tex} \mathrm { F } _ { 3 } - \mathrm { F } _ { 1 } + \mathrm { F } _ { 2 } {/tex}

##### Explanation Q 21.

Correct4

Incorrect-1

A long solenoid carrying a current produces a magnetic field {tex} B {/tex} along its axis. If the current is double and the number of turns per {tex} \mathrm { cm } {/tex} is halved, the new value of the magnetic field is

A

4{tex} B {/tex}

B

{tex} B / 2 {/tex}

{tex} B {/tex}

D

{tex} 2B {/tex}

##### Explanation Q 22.

Correct4

Incorrect-1

A particle of charge {tex} q {/tex} and mass {tex} m {/tex} moves in a circular orbit of radius r with angular speed {tex} \omega . {/tex} The ratio of the magnitude of its magnetic moment to that of its angular momentum depends on

A

{tex} \omega {/tex} and {tex} q {/tex}

B

{tex} \omega , q {/tex} and {tex} m {/tex}

{tex} q {/tex} and {tex} m {/tex}

D

{tex} \omega {/tex} and {tex} m {/tex}

##### Explanation Q 23.

Correct4

Incorrect-1

A current loop in a magnetic field

A

can be in equilibrium in one orientation

B

can be in equilibrium in two orientations, both the equilibrium states are unstable

can be in equilibrium in two orientations, one stable while the other is unstable

D

experiences a torque whether the field is uniform or non-uniform in all orientations

##### Explanation Q 24.

Correct4

Incorrect-1

Two long parallel wires P and Q are held perpendicular to the plane of paper with distance of 5 m between them. If Pand Q carry current of 2.5 amp. and 5 amp. respectively inthe same direction, then the magnetic field at a point half-way between the wires is

A

{tex} \mu _ { 0 } / 17 {/tex}

B

{tex} \sqrt { 3 } \mu _ { 0 } / 2 \pi {/tex}

{tex} \mu _ { 0 } / 2 \pi {/tex}

D

3{tex} \mu _ { 0 } / 2 \pi {/tex}

##### Explanation Q 25.

Correct4

Incorrect-1

A very long straight wire carries a current I. At the instant when a charge {tex} + Q {/tex} at point {tex} P {/tex} has velocity {tex} \vec { v } {/tex} as shown, the force on the charge is along {tex} O Y {/tex}

B

opposite to {tex} O Y {/tex}

C

along {tex} O X {/tex}

D

opposite to {tex} O X {/tex}

##### Explanation 