Magnetism and Matter

The main topic of this chapter includes - Ampere's Circuital Law, magnetic field lines, and Gauss's Law.

In JEE Main exam, it is a significant chapter. There can be 6 to 8 questions from this chapter, a weightage of nearly 6.6%.

The exact weightage varies from year to year. This chapter comes under a broader category which can be "Magnetism" or "Modern Physics". In NEET exam, the chapter's weightage is low to moderate and there can be 6-7% of questions from this chapter.

The chapter is one of the small and easy chapter of class 12 Physics. It includes - properties of magnetic materials, magnetic dipoles, and Earth's magnetic field.

When the electric charges moves, it creates attraction or repulsion. It creates magnetic forces and fields and called magnetism. The term "magnetism and matter" talks about the way magnetic forces and matter interact.

According to Gauss's law for magnetism, the net magnetic flux through any closed surface is zero.

$?\mathbf{B}\cdot dA=0$

It states that all magnetic field lines must enter and exit from a surface. In this way, it differs from electric charges, which can exist independently as positive and negative.

Magnetism is the force exerted by a magnet. It comes when the magnet attracts or repulses an object. For example, a magnet sticks to certain objects because the magnetic force or magnetism pulls it.

M = 9.85*10? ² A/m²

I = 5*10? kg-m²

T = 5s/10osc = 0.5 sec

B =?

T = 2π√ (I/MB)

B = 4π²I/ (MT²) = (4*9.85*5*10? )/ (9.85*10? ² * 0.5²)

B = (20*10? )/ (10? ² * 0.25) = 800*10? = 0.8*10? ³ T = 8mT

When a soft ferromagnetic substance is placed in external magnetic field, the size of domain lying in the opposite direction of external magnetic field increases while size of domain lying in the opposite direction of field decreases if field is weak. However, if field is strong then the domain rotate in the direction of external magnetic field due to strong torque.

True dip is less than the apparent dip.