The magnetic field of the earth’ can be modelled by that of a point dipole placed at the centre of the earth. The dipole axis makes an angle of 11.3° with the axis of the earth. At Mumbai, the declination is nearly zero. Then
(a) The declination varies between 11,3°W to 11.3°E
(b) The least declination is 0°
(c) The plane defined by dipole axis and the earth axis passes through Greenwich
(d) Declination averaged over the earth must be always negative

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.