The corecivity of a small magnet where the ferromagnet gets demagnetized is 3 × 10³ A/m. The current required to be passed in a solenoid of length 10 cm and number of turns 100, so that the magnet gets demagnetized when inside the solenoid is:

H = nI/L
where H is the magnetic field strength, n is the number of turns, I is the current, and L is the length of the solenoid.
Given:
Corecivity (H) = 3 × 10³ A/m
Number of turns (n) = 100
Length of solenoid (L) = 10 cm = 0.1 m
We need to find the current (I) required to demagnetize the magnet.
Substituting the given values into the equation:
3 × 10³ A/m = (100 × I) / 0.1 m
3 × 10³ A/m = 1000 I
I = (3 × 10³ A/m) / 1000
I = 3 A
Therefore, the current required to be passed in the solenoid is 3A.