# NCERT Physics Class 12 Exemplar Ch 5 Magnetism and Matter Part 6

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## Long Answer Types Questions

Q.21 Verify the Ampere’s law for magnetic field of a point dipole of dipole moment . Take as the closed curve running clockwise along

(i) The axis from

(ii) Along the quarter circle of radius R and center at the origin, in the first quadrant of plane;

(iii) Along the axis from , and

(iv) Along the quarter circle of radius and center at the origin in the first quadrant of plane.

Solution:

(i) Along axis

(ii) Along the quarter circle of radius

(iii) Along x-axis

(iv) Along the quarter circle of radius

Add

Q.22 What are the dimensions of , the magnetic susceptibility? Consider an atom. Guess an expression for , upto a constant by constructing a quantity of dimensions of , out of parameters of the atom: and . Here, is the electronic mass, is electronic velocity, is Bohr radius. Estimate the number so obtained and compare with the value of for many solid materials.

Solution:

is dimensionless.

depends on magnetic moment induced when is turned on. couples to atomic electrons through its charge The effect on is via current which involves another factor of . The combination does not depend on the “charge” dimension.