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 $$\mathrm{I}=4 \mathrm{~A}$$ 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)

Two long, straight wires carry equal currents in opposite directions as shown in figure. The separation between the wires is $$5.0 \mathrm{~cm}$$. The magnitude of the magnetic field at a point $$\mathrm{P}$$ midway between the wires is _______ $$\mu \mathrm{T}$$

(Given : $$\mu_0=4 \pi \times 10^{-7} \mathrm{TmA}^{-1}$$)

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

A straight wire $$\mathrm{AB}$$ of mass $$40 \mathrm{~g}$$ and length $$50 \mathrm{~cm}$$ is suspended by a pair of flexible leads in uniform magnetic field of magnitude $$0.40 \mathrm{~T}$$ as shown in the figure. The magnitude of the current required in the wire to remove the tension in the supporting leads is ___________ A.

$$\left(\right.$$ Take $$g=10 \mathrm{~ms}^{-2}$$ ).