An electron having mass $9.1\times {10}^{-31} \mathrm{kg},$ charge $1.6\times {10}^{-19} \mathrm{C}$ and moving with the velocity of ${10}^6 \mathrm{m} {\mathrm{s}}^{-1}$ enters a region where magnetic field exists. If it describes a circle of radius $0.2 \mathrm{m}$ then intensity of magnetic field must be _____ $\times {10}^{-5} \mathrm{T}.$

Two parallel very long straight wires carrying current of $5 \mathrm{A}$ each are kept at a separation of $1 \mathrm{m}.$ If the currents are in the same direction, the force per unit length between them is _____ $\mathrm{N} {\mathrm{m}}^{-1}. \left({\mu }_0=4\pi \times {10}^{-7} \mathrm{SI}\right)$

A very long straight wire of radius $r$ carries current $I$. Intensity of magnetic field $B$ at a point lying at a perpendicular distance $a$ from the axis is $\propto$ _____ $(\text{where} a<r)$.

Two very long straight wires are set parallel to each other. Each carries a current $I$ in the same direction and the separation between them is $2r.$ The intensity of the magnetic field at point $P$ as shown in the figure is _________.