Magnetic Force is a force that attracts certain metal objects towards a magnet. Some examples of metallic magnets include iron fillings, etc.

A magnetic field is the area around a magnetic material or moving electric charge within which acts the force of magnetism.

There are three sources of magnetic fields. They are as follows:

• Conductors that carry current: An electric current generates a magnetic field. A pattern of circular field lines surrounding a wire may be used to view this magnetic field.
• Magnets that are permanent: Permanent magnets are the most frequent magnetic field generators. Permanent magnetic fields, on the other hand, are difficult to calculate and need a thorough grasp of ferromagnetic processes. A permanent magnet is an example of a compass needle.
• Electromagnets: A basic electromagnet is made out of a wire coil wrapped around an iron core. The magnetic field generated is aided by the iron core. The strength of the magnetic field generated and the amount of current through the winding are proportional.

When a force acting on a particle has a component in the particle's direction of motion, it is said to perform work. The magnetic force acts perpendicular to the particle's motion when we have a charged particle with a charge, q, travelling in a uniform magnetic field of size, B. The magnetic force does not work on the particle, and, hence, there is no change detected in the particle's velocity.

The formula is:

F = q(v x B)

The magnetic force operates as a centripetal force when it is directed towards the object's centre of circular motion. The article describes a circle if v and B are perpendicular to each other.

When the electric field, magnetic field, and charge motion are all perpendicular to one another, they are referred to as crossed fields, and the forces generated by the electric and magnetic fields will act in opposing directions. As a result, the Lorentz force F will be as follows:

F = qEî+(qvî x Bk̂) = qEĵ - qVBî = q(E - vB)ĵ

When the strength of electric and magnetic fields are varied to get the forces due to equal electric and magnetic fields (FE = FB), the charge can move in the field without deflection.

qE = qvB

∴ v = E/B

According to Biot-Savart Law, carrying a current I via a tiny current-carrying conductor of length dl is an elementary source of the magnetic field. The force on a second identical conductor may be simply stated in terms of the first's magnetic field dB. Biot and Savart were the first to hypothesise the relationship between magnetic field dB and current I, length element dl size and orientation, and distance r.

If we consider a conducting element dl of the loop, the magnetic field at point P can be given by Biot-Savart Law:

Since dl is a small element of a circular loop, the summation of dl leads to 2πR, the loop circumference. Therefore, the magnetic field becomes:

When x = 0, we get the magnetic field at the centre of the current-carrying loop. The formula is given below:

As stated by Ampere’s law, the magnetic field created by an electric current is proportional to the size of that electric current with a constant of proportionality equal to the permeability of free space.

According to this law, the line integral of the magnetic field surrounding the closed-loop equals the number of times the algebraic sum of currents passes through the loop.

Solved example:

Consider a long wire carrying current in Amps. How much is the magnetic field at a distance r?

If the magnetic field is integrated along the blue route, it must equal the current contained, I, according to the second equation.

Due to symmetry, the magnetic field does not fluctuate at a distance r. In figure 1, the route length (in blue) is equal to the diameter of a circle, 2pir.

When a constant value H is added to the magnetic field, the equation’s left side looks like this:

A solenoid is an electromagnet that uses a coil fitted into a densely packed helix to create a regulated magnetic field. When an electric current is fed through the coil, it may be configured to generate a homogeneous magnetic field in a volume of space.

A toroid is a solenoid twisted into a circular form that closes into a loop-like structure. It is a hollow circular ring made up of several turns of enamelled wire that are tightly coiled with very little space between them.

Consider a system wherein there are two parallel current-carrying conductors separated by a distance d, one of which is carrying current I1 and the other is carrying current I2. Due to conductor 1, conductor 2 encounters the same magnetic field at every point along its length.

From the Ampere’s circuital law, the magnitude of the field due to the first conductor can be given by,

Ba = μ0I1/ 2πd

In moving charges and magnetism NCERT solutions, as the dimensions of the source are reduced to zero while the magnetic moment remains constant, a magnetic dipole is the limit of either a closed loop of electric current or a pair of poles. We'll now prove that a constant current I flowing around a rectangular loop in a uniform magnetic field produces torque. It is not subjected to a net force. In a homogeneous electric field, its behaviour is comparable to that of an electric dipole.

A moving coil galvanometer is an electromagnetic instrument for measuring low current levels. It is made up of permanent horseshoe magnets, a coil, a soft iron core, a hinged spring, a non-metallic frame, a scale, and a pointe.

1. A circular coil of wire consisting of 100 turns, each of radius 8.0 cm carries a current of 0.40 A. What is the magnitude of the magnetic field B at the centre of the coil?

The number of turns on the coil (n) is 100

The radius of each turn (r) is 8 cm or 0.08 m

The magnitude of the current flowing in the coil (I) is 0.4 A

The magnitude of the magnetic field at the centre of the coil can be obtained by the following relation:

IBI = μ0 2πnI/4πr

= 3.14×10-4T

1. Why should I refer to MSVgo's NCERT Solutions for Class 12 Physics Chapter 4?

The notes are prepared by subject experts and include illustrative examples with in-depth explanations. They help students score good marks in their competitive exams.

2. Is the NCERT Solutions for Class 12 Physics Chapter 4 the best reference guide for the students?

Yes, moving charges and magnetism class 12 NCERT solutions is the best reference guide for students.

3. Discuss the pattern of the questions from this chapter.

The questions from this chapter are often amalgamated with concepts from other chapters in competitive exams. Questions related to the Bion-savart’s law are topics of interest to examiners.