Two short magnets of equal dipole moments $$M$$ are fastened perpendicularly at their centres. The magnitude of the magnetic field at a distance $$d$$ from the centre on the bisector of the right angle is ($$\mu_0=$$ Permeability of free space)
A steel wire of length $$l$$ and magnetic moment $$M$$ is bent into a semicircular arc of radius $$R$$. The new magnetic moment is
A magnetic needle free to rotate in a vertical plane parallel to the magnetic meridian has its north tip pointing down at $$30^{\circ}$$ with the horizontal. The horizontal component of the earth's magnetic field at the place is 0.3 G . Then the magnitude of the earth's magnetic field at the location is
A compass needle oscillates 20 times per minute at a place where the dip is $$45^{\circ}$$ and the magnetic field is $$B_1$$. The same needle oscillates 30 times per minute at a place where the dip is $$30^{\circ}$$ and magnetic field is $$B_2$$. Then, $$B_1: B_2$$ is