A bar magnet has coercivity $4\times 10^{3}A{m}^{-1}$. It is placed in a solenoid having $40$ turns per cm and is $1.2m$ long. The current carried by the solenoid to demagnetize  the bar magnet is :

The pole strength of a 12 cm long bar magnet is 20 A.m. The magnetic induction at a point 10 cm along from the centre of the magnet on its axial line is

A bar magnet of $5$ cm long having a pole strength of $20$ A.m. is deflected through $30^0$ from the magnetic meridian. If $H=\frac{320}{4\pi }$ A/m, the deflecting couple is