Question

The coercive force for a certain permanent magnet is 4.0 x 10⁴A/m. This magnet is placed inside a long solenoid of 40turns/cm and a current is passed in the solenoid to demagnetise it completely. Find the current.

Answer 1

B = μ₀ni,  H = B/μ₀

Given n = 40turn/cm = 4000turns/m

=> H = ni

H = 4 × 10⁴A/m

=> i = H/n = (4 x 10⁴)/4000 = 10A.