An electron revolves in a circle of radius $0.4\,\text{\AA}$ with a speed of $10^6\,\text{m/s}$ in a hydrogen atom. The magnetic field produced at the centre of the orbit due to the motion of the electron (in Tesla) is: [$\mu_0 = 4\pi \times 10^{-7}\,\text{H/m}$, charge on the electron $= 1.6 \times 10^{-19}\,\text{C}$]