The ratio of magnetic field at the centre of a current carrying circular coil to its magnetic moment is $$x$$, if the current and the radius both are doubled. The new ratio will become

Two long straight parallel wires are a distance $$d$$ part. They carry steady equal currents flowing out of the plane of the paper. The variation of magnetic field $B$ along the line $$x x^{\prime}$$ is given by

A toroid has 500 turns per meter length. If it carries a current of $$2 \mathrm{A}$$, the magnetic energy density inside the toroid is

In a cyclotron a charged particle