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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 experienced teachers.

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Magnetic Effects of Current and Magnetism

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Q 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 about 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

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Q 2. A portion of a conductive wire is bent in the form of a semicorcle of radius r as shown below in fig. At the centre of semicircle, the magnetic induction will be

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

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Q 3. 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 is 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

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Q 4. 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 accelerate protons (mass = m ). 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

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Q 5. If we double the radius of a coil keeping the current through it unchanged, then the magnetic field at any point at a large distance from the centre becomes approximately

A

double

B

three times

four times

D

one-fourth

Explanation

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Q 6. 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

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Q 7. If in a circular coil {tex} A {/tex} of radius {tex} R , {/tex} current {tex} I {/tex} is flowing and in another coil {tex} B {/tex} of radius 2{tex} R {/tex} a current 2{tex} I {/tex} is flowing, then the ratio of the magnetic fields {tex} B _ { A } {/tex} and {tex} B _ { B } , {/tex} produced by them will be

1

B

2

C

1/2

D

4

Explanation

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Q 8. A charged particle moves through a magnetic field perpendicular to its direction. Then

A

kinetic energy changes but the momentum is constant

the momentum changes but the kinetic energy is constant

C

both momentum and kinetic energy of the particle are not constant

D

both momentum and kinetic energy of the particle are constant

Explanation



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Q 9. The deflection in a galvanometer falls from 50 division to 20 when a 12 ohm shunt is applied. The galvanometer resistance is

18 ohm

B

36 ohm

C

24 ohm

D

30 ohm

Explanation

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Q 10. When a long wire carrying a steady current is bent into a circular coil of one turn, the magnetic induction at its centre is B. When the same wire carrying the same current is bent to form a circular coil of n turns of a smaller radius, the magnetic induction at the centre will be

A

{tex} \mathrm { B } / \mathrm { n } {/tex}

B

{tex} \mathrm { nB } {/tex}

C

{tex} \mathrm { B } / \mathrm { n } ^ { 2 } {/tex}

{tex} \mathrm { n } ^ { 2 } \mathrm { B } {/tex}

Explanation

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Q 11. The magnetic field due to a current carrying circular loop of radius 3{tex} \mathrm { cm } {/tex} at a point on the axis at a distance of 4{tex} \mathrm { cm } {/tex} from the centre is 54{tex} \mu \mathrm { T } {/tex} . What will be its value at the centre of loop?

A

125{tex} \mu \mathrm { T } {/tex}

B

150{tex} \mu \mathrm { T } {/tex}

250{tex}\mu \mathrm {T}{/tex}

D

75{tex} \mu \mathrm { T } {/tex}

Explanation

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Q 12. A charge moving with velocity v in {tex} \mathrm { X } {/tex} -direction is subjected to a field of magnetic induction in negative {tex} \mathrm { X } {/tex} -direction. As a result, the charge will

remain unaffected

B

start moving in a circular path {tex} \mathrm { Y } - \mathrm { Z } {/tex} plane

C

retard along X-axis

D

move along a helical path around x-axis

Explanation

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Q 13. An electron travelling with a speed u along the positive {tex} x {/tex} -axis enters into a region of magnetic field where {tex} B = - B _ { 0 } \hat { k } ( x /> 0 ) . {/tex} It comes out of the region with speed {tex} \mathrm { v } {/tex} then

A

{tex} v = u {/tex} at {tex} y > 0 {/tex}

{tex} v = u {/tex} at {tex} y < 0 {/tex}

C

{tex} v > u {/tex} at {tex} y > 0 {/tex}

D

{tex} v > u {/tex} at {tex} y < 0 {/tex}

Explanation

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Q 14. If an ammeter is to be used in place of a voltmeter, then we must connect with the ammeter a

A

low resistance in parallel

B

high resistance in parallel

high resistance in series

D

low resistance in series

Explanation

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Q 15. An infinite straight conductor carrying current 2{tex} \mathrm { I } {/tex} is split into a loop of radius r as shown in fig. The magnetic field at
the centre of the coil is

A

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

B

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

C

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

zero

Explanation

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Q 16. A parallel plate capacitor of area 60{tex} \mathrm { cm } ^ { 2 } {/tex} and separation 3{tex} \mathrm { mm } {/tex} is charged initially to 90{tex} \mu \mathrm { C } {/tex} . If the medium between the plate gets slightly conducting and the plate loses the charge initially at the rate of {tex} 2.5 \times 10 ^ { - 8 } \mathrm { C } / \mathrm { s } {/tex} , then what is the magnetic field between the plates?

A

{tex} 2.5 \times 10 ^ { - 8 } \mathrm { T } {/tex}

B

{tex} 2.0 \times 10 ^ { - 7 } \mathrm { T } {/tex}

C

{tex} 1.63 \times 10 ^ { - 11 } \mathrm { T } {/tex}

Zero

Explanation

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Q 17. Four wires, each of length 2.0 m, are bent into four loops P,Q, R and S and then suspended in a uniform magnetic field. If the same current is passed in each, then the torque will be maximum on the loop

A

{tex}\mathrm P {/tex}

B

{tex}\mathrm Q {/tex}

C

{tex} \mathrm { R } {/tex}

{tex} \mathbf { S } {/tex}

Explanation

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Q 18. A certain region has an electric field {tex} \vec{E} (2\hat{{ \mathrm { i } }} - 3\hat{ \mathrm { j } }){/tex} N / C and a uniform magnetic field {tex}\vec{B} (5\hat{{ \mathrm { i } }} + 3\hat{ \mathrm { j } } + 4\hat{ \mathrm { k } })T{/tex}. The force experienced by a charge 1C moving with velocity {tex}(\hat{{ \mathrm { i } }} + 2\hat{ \mathrm { j } }) ms^{–1}{/tex} is

{tex} ( 10 \hat { \mathrm { i } } - 7 \hat { \mathrm { j } } - 7 \hat { \mathrm { k } } ) {/tex}

B

{tex} ( 10 \hat { \mathrm { i } } + 7 \hat { \mathrm { j } } + 7 \hat { \mathrm { k } } ) {/tex}

C

{tex} ( - 10 \hat { \mathrm { i } } + 7 \hat { \mathrm { j } } + 7 \hat { \mathrm { k } } ) {/tex}

D

{tex} ( 10 \hat { \mathrm { i } } + 7 \hat { \mathrm { j } } - 7 \hat { \mathrm { k } } ) {/tex}

Explanation

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Q 19. A galvanometer of resistance 100{tex} \Omega {/tex} gives a full scale deflection for a current of {tex} 10 ^ { - 5 } {/tex} A. To convert it into a ammeter capable of measuring upto 1 A, we should connect a resistance of

A

1{tex} \Omega {/tex} in parallel

{tex} 10 ^ { - 3 } \Omega {/tex} in parallel

C

{tex} 10 ^ { 5 } \Omega {/tex} in series

D

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

Explanation

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Q 20. A square loop, carrying a steady current I, is placed in a horizontal plane near a long straight conductor carrying a steady current {tex} I_ { 1 } {/tex} at a distance d from the conductor as shown in figure. The loop will experience

A

a net repulsive force away from the conductor

B

a net torque acting upward perpendicular to the horizontal plane

C

a net torque acting downward normal to the horizontal plane

a net attractive force towards the conductor

Explanation



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Q 21. Two coaxial solenoids of different radius carry current {tex}I{/tex} in the same direction. {tex} \vec { F } _ { 1 } {/tex} be the magnetic force on the inner solenoid due to the outer one and {tex} \vec { F } _ { 2 } {/tex} be the magnetic force on the outer solenoid due to the inner one. Then:

A

{tex} \overrightarrow { \mathrm { F } } _ { 1 } {/tex} is radially in wards and {tex} \overrightarrow { \mathrm { F } _ { 2 } } = 0 {/tex}

B

{tex} \overrightarrow { \mathrm { F } _ { 1 } } {/tex} is radially outwards and {tex} \overrightarrow { \mathrm { F } _ { 2 } } = 0 {/tex}

{tex} \overrightarrow { \mathrm { F } _ { 1 } } = \overrightarrow { \mathrm { F } _ { 2 } } = 0 {/tex}

D

{tex} { \mathrm { \vec{F} } _ { 1 } } {/tex} is radially inwards and {tex} { \mathrm { \vec{F} } _ { 2 } } {/tex} is radially outwards

Explanation

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Q 22. A beam of electrons is moving with constant velocity in a region having simultaneous perpendicular electric and magnetic fields of strength 20{tex} \mathrm { Vm } ^ { - 1 } {/tex} and 0.5 T respectively at right angles to the direction of motion of the electrons. Then the velocity of electrons must be

A

8{tex} \mathrm { m } / \mathrm { s } {/tex}

B

20{tex} \mathrm { m } / \mathrm { s } {/tex}

40{tex} \mathrm { m } / \mathrm { s } {/tex}

D

{tex} \frac { 1 } { 40 } \mathrm { m } / \mathrm { s } {/tex}

Explanation

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Q 23. The magnetic flux density {tex} \mathrm { B } {/tex} at a distance {tex} \mathrm { R} {/tex} from a long straight wire carrying a steady current varies with {tex} \mathrm { r } {/tex} as

A

B

D

Explanation

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Q 24. The AC voltage across a resistance can be measured using a :

A

hot wire voltmeter

moving coil galvanometer

C

potential coil galvanometer

D

moving magnet galvanometer

Explanation

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Q 25. Two identical magnetic dipoles of magnetic moments {tex} 1.0 \mathrm { A } \mathrm { m } ^ { 2 } {/tex} each, placed at a separation of 2{tex} \mathrm { m } {/tex} with their axis perpendicular to each other. The resultant magnetic field at point midway between the dipole is

A

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

{tex} \sqrt { 5 } \times 10 ^ { - 7 } \mathrm { T } {/tex}

C

{tex} 10 ^ { - 7 } \mathrm { T } {/tex}

D

{tex} 2 \times 10 ^ { - 7 } \mathrm { T } {/tex}

Explanation