CGPET 2021 Solved Paper

Given, length of steel wire = l

Let each pole strength is m, then magnetic moment of wire,
M=m.l ......(i)
On bending a wire, its' pole strength does not change.
Let R is the radius of semicircular arc.
Then, new magnetic moment,
M′=

m

(2R)

....(ii)
But l=πR
∴ R=

1

π

From eq. (ii) we get
M′=m.2

l

π

M′=

2M

π

[From eq.(i)]