Moving Charges and Magnetism NEET Questions with Solutions

Q: How many questions come from Moving Charges and Magnetism in NEET 2027?

You can expect 1 to 2 questions in NEET 2027. The chapter has high PYQ frequency. Lorentz force, motion in magnetic field (radius and period), Biot-Savart for straight wire and circular coil, solenoid, and torque on a current loop are favourites.

Q: What is the Lorentz force?

A charge q moving with velocity v in a magnetic field B feels a force F equals q v cross B. The magnitude is q v B sin theta, where theta is the angle between v and B. Direction is perpendicular to both v and B (right-hand rule). The force does no work because it is always perpendicular to v.

Q: What is the radius of a charged particle in a uniform B?

When v is perpendicular to B, the particle moves in a circle. Magnetic force provides the centripetal force: q v B equals m v squared over r, giving r equals m v over (q B). The time period T equals 2 pi m over (q B), independent of speed.

Q: What is the Biot-Savart law?

It gives the magnetic field at point P due to a small current element I dL: dB equals (mu_0 over 4 pi) times (I dL cross r unit vector) over r squared. Direction is perpendicular to both dL and the line from element to point. For a finite wire or loop, integrate over the geometry.

Q: What is the magnetic field inside a long solenoid?

B equals mu_0 n I, where n is the number of turns per unit length and I is the current. The field is uniform along the axis and zero outside (ideal long solenoid). At the END of a finite solenoid, the field is half this value.

Q: What is the force between two parallel current-carrying wires?

Two wires carrying currents I_1 and I_2 in the same direction attract each other. In opposite directions, they repel. Force per unit length is f equals (mu_0 I_1 I_2) over (2 pi d), where d is the separation. This is the definition of the ampere: 1 A is the current that produces 2 times 10 to the minus 7 N per metre between two wires 1 m apart.

Q: What is the torque on a current loop in a magnetic field?

A coil of N turns, area A carrying current I has a magnetic dipole moment m equals N I A (perpendicular to the coil). In a uniform field B, torque is tau equals m cross B, magnitude m B sin theta. This is the principle behind the moving coil galvanometer and electric motor.

Question 1

Force on a charge q moving with velocity v in field B is:

Accepted Answer

[math]

Question 2

Radius of a charged particle's circular path in B field:

Accepted Answer

[math]

Question 3

Magnetic field at distance [math] from an infinite straight wire of current I:

Accepted Answer

[math]

Question 4

Field at centre of a circular coil with N turns of radius R carrying I:

Accepted Answer

[math]

Question 5

Magnetic field inside a long solenoid is:

Accepted Answer

Both b and c

Question 6

Two parallel wires carrying same direction currents:

Accepted Answer

Attract

Question 7

Cyclotron frequency for a particle with charge q, mass m in field B:

Accepted Answer

[math]

Question 8

Maximum torque on a current loop with magnetic moment m in field B:

Accepted Answer

[math]

Question 9

Period of circular motion in B field depends on:

Accepted Answer

m/q ratio and B

Question 10

A charge moves parallel to magnetic field. Force on it:

Accepted Answer

Zero

Question 11

Force per unit length between two parallel wires (1 A each, 1 m apart):

Accepted Answer

[math] N/m

Question 12

Biot-Savart law for [math] at perpendicular distance [math] from element [math] is:

Accepted Answer

[math]

Question 13

A coil of 50 turns of 0.1 m radius carries 2 A. Field at centre:

Accepted Answer

[math] T

Question 14

Field at 10 cm from a wire carrying 5 A:

Accepted Answer

[math] T

Question 15

A solenoid has 200 turns per metre and carries 2 A. Field inside is:

Accepted Answer

[math] T

Question 16

A proton (m, q) and electron (m_e, e) enter the same B perpendicular at the same speed. Ratio of radii r_p/r_e:

Accepted Answer

[math]

Question 17

Magnetic moment of a coil:

Accepted Answer

[math]

Question 18

A wire of length 1 m carrying 5 A is in a 0.2 T field perpendicular to it. Force on the wire:

Accepted Answer

1 N

Question 19

Cyclotron cannot accelerate:

Accepted Answer

Electrons

Question 20

Two parallel wires 0.5 m apart carry 4 A each in opposite directions. Force per unit length:

Accepted Answer

[math] N/m, repulsive

Question 21

Field on the axis of a circular coil at [math] (R is the coil radius) in terms of B at centre:

Accepted Answer

[math]

Question 22

A current element points along x. Field at a point on the y-axis is along:

Accepted Answer

z

Question 23

A coil of 100 turns, area 5 cm² carries 1 A in a 0.1 T field at θ = 30°. Torque:

Accepted Answer

[math] N·m

Question 24

Magnetic force on a stationary charge in a magnetic field:

Accepted Answer

Zero

Question 25

A particle of charge [math] and mass [math] moves in a circle in B with kinetic energy [math]. Radius:

Accepted Answer

[math]

Question 26

Magnetic field at the centre of an arc of radius R subtending angle θ at the centre:

Accepted Answer

[math]

Question 27

Field at the END of a long solenoid compared to inside:

Accepted Answer

Half

Question 28

The unit of [math] is:

Accepted Answer

T·m/A

Question 29

Definition of 1 ampere (old): force per unit length is [math] N/m between two wires at:

Accepted Answer

1 m apart

Question 30

Maximum kinetic energy in a cyclotron of radius R is:

Accepted Answer

[math]

Question 31

A square loop of side [math] carries I in a field B parallel to its plane. Torque:

Accepted Answer

[math]

Question 32

In a Helmholtz coil pair (two coils of radius R, separation R, same I), the field at the midpoint is:

Accepted Answer

[math]

Moving Charges and MagnetismNEET Physics · Class 12 · NCERT Chapter 4

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Moving Charges and MagnetismNEET Physics · Class 12 · NCERT Chapter 4

1NEET 2018EasyForce on a charge q moving with velocity v in field B is:

2NEET 2020MediumRadius of a charged particle's circular path in B field:

3NEET 2022MediumMagnetic field at distance r from an infinite straight wire of current I:

4NEET 2024MediumField at centre of a circular coil with N turns of radius R carrying I:

5NEET 2017EasyMagnetic field inside a long solenoid is:

6NEET 2019MediumTwo parallel wires carrying same direction currents:

7NEET 2021MediumCyclotron frequency for a particle with charge q, mass m in field B:

8NEET 2023MediumMaximum torque on a current loop with magnetic moment m in field B:

9NEET 2018MediumPeriod of circular motion in B field depends on:

10NEET 2020MediumA charge moves parallel to magnetic field. Force on it:

11NEET 2022MediumForce per unit length between two parallel wires (1 A each, 1 m apart):

12NEET 2024MediumBiot-Savart law for dB at perpendicular distance r from element IdL is:

13NEET 2017MediumA coil of 50 turns of 0.1 m radius carries 2 A. Field at centre:

14NEET 2019MediumField at 10 cm from a wire carrying 5 A:

15NEET 2021MediumA solenoid has 200 turns per metre and carries 2 A. Field inside is:

16NEET 2023MediumA proton (m, q) and electron (m_e, e) enter the same B perpendicular at the same speed. Ratio of radii r_p/r_e:

17NEET 2018MediumMagnetic moment of a coil:

18NEET 2020MediumA wire of length 1 m carrying 5 A is in a 0.2 T field perpendicular to it. Force on the wire:

19NEET 2022MediumCyclotron cannot accelerate:

20NEET 2024MediumTwo parallel wires 0.5 m apart carry 4 A each in opposite directions. Force per unit length:

21NEET 2017MediumField on the axis of a circular coil at x=R (R is the coil radius) in terms of B at centre:

22NEET 2019MediumA current element points along x. Field at a point on the y-axis is along:

23NEET 2021MediumA coil of 100 turns, area 5 cm² carries 1 A in a 0.1 T field at θ = 30°. Torque:

24NEET 2023MediumMagnetic force on a stationary charge in a magnetic field:

25NEET 2018MediumA particle of charge +q and mass m moves in a circle in B with kinetic energy K. Radius:

26NEET 2020MediumMagnetic field at the centre of an arc of radius R subtending angle θ at the centre:

27NEET 2022EasyField at the END of a long solenoid compared to inside:

28NEET 2024MediumThe unit of μ0​ is:

29NEET 2017MediumDefinition of 1 ampere (old): force per unit length is 2×10−7 N/m between two wires at:

30NEET 2019MediumMaximum kinetic energy in a cyclotron of radius R is:

31NEET 2021MediumA square loop of side a carries I in a field B parallel to its plane. Torque:

32NEET 2023MediumIn a Helmholtz coil pair (two coils of radius R, separation R, same I), the field at the midpoint is:

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