Hello Abdul Raza,

A semi circular magnet has magnetic movement as M.

Magnetic movement= Pole strength * distance between the poles

For the semi circular consider the radius as r. so the distance between two poles becomes the diameter which equals 2r. then M1= m*(2r)

if it is made into straight line then the distance becomes pie*r so now M2=m*(pie*r)

if you divide M1 and M2.

then you will notice that M2=(pie/2)M1

if the semicircular magnet of magnet movement M is made into straight line then its magnetic movement becomes (pie/2)*M.