A planet has magnetic dipole moment of $27 \times 10^{22} \mathrm{~A}-\mathrm{m}^2$. If the radius of the planet is 300 km , what would be the magnetic field at its equator? $\left(\right.$ use,$\left.\frac{\mu}{4 \pi}=10^{-7}\right)$

Which of the following is desirable for making permanent magnets?

A short bar magnet placed with its axis at $30^{\circ}$ with an external field of 800 G experiences a torque of 0.016 Nm . The magnetic moment of the bar magnet is

A solenoid has a core of a material with relative permeability $\frac{800}{\pi}$. The windings of the solenoid are insulated from the core and carry current of 2 A . If the number of turns is 1000 per metre, find the magnetic field $B$.