A permanent magnet has a coercive force of 4.0 10^4 A m ⁻¹ . It is inserted into a long solenoid having 40 turns/cm. To completely demagnetize the magnet, a current is sent through the solenoid. Determine this current.

Step-by-step solution

The coercive force H_c is the magnetic field intensity required to completely demagnetize the magnet. For a long solenoid, the magnetic field intensity H is given by H = nI , where n is the number of turns per unit length and I is the current. Given: H_c = 4.0 10^4 A m ⁻¹ n = 40 turns/cm = 4000 turns/m Equating H to H_c to find the required current: nI = H_c 4000 I = 4.0 10^4 I = 40000 4000 = 10 A