# NEET

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.

## Biology

Magnetic Effects of Current and Magnetism

Correct Marks 4

Incorrectly Marks -1

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

Correct Marks 4

Incorrectly Marks -1

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

Correct Marks 4

Incorrectly Marks -1

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

Correct Marks 4

Incorrectly Marks -1

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

Correct Marks 4

Incorrectly Marks -1

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

Correct Marks 4

Incorrectly Marks -1

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

Correct Marks 4

Incorrectly Marks -1

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

Correct Marks 4

Incorrectly Marks -1

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

Correct Marks 4

Incorrectly Marks -1

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

Correct Marks 4

Incorrectly Marks -1

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

Correct Marks 4

Incorrectly Marks -1

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

Correct Marks 4

Incorrectly Marks -1

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

Correct Marks 4

Incorrectly Marks -1

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

Correct Marks 4

Incorrectly Marks -1

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

Correct Marks 4

Incorrectly Marks -1

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

Correct Marks 4

Incorrectly Marks -1

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

Correct Marks 4

Incorrectly Marks -1

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

Correct Marks 4

Incorrectly Marks -1

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

Correct Marks 4

Incorrectly Marks -1

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

Correct Marks 4

Incorrectly Marks -1

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

Correct Marks 4

Incorrectly Marks -1

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

Correct Marks 4

Incorrectly Marks -1

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

Correct Marks 4

Incorrectly Marks -1

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

Correct Marks 4

Incorrectly Marks -1

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

Correct Marks 4

Incorrectly Marks -1

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}