When the current flowing in a circular coil is doubled and the number of turns of the coil in it is halved, the magnetic field at its centre will become

What is the magnetic field at a distance $R$ from a coil of radius $r$ carrying current $I$ ?

A very long conducting wire is bent in a semicircular shape from $A$ to $B$ as shown in figure. The magnetic field at point $P$ for steady current configuration is given by:

The magnetic field at the centre of a wire loop formed by two semicircular wires of radii $R_1=2 \pi\  \mathrm{m}$ and $R_2=4 \pi\  \mathrm{m}$ carrying current $I=4 \mathrm{~A}$ as per figure given below is $\alpha \times 10^{-7} \mathrm{~T}$. The value of $\alpha$ is___________ (Centre $\mathrm{O}$ is common for all segments)

The following statement is false for Helmholtz coils

An electron in a hydrogen atom revolves around its nucleus with a speed of $6.76 \times 10^6\,ms ^{-1}$ in an orbit of radius $0.52\,\mathring A$. The magnetic field produced at the nucleus of the hydrogen atom is $......T$.