The radiation corresponding to 32 transition of a hydrogen atom falls on a gold surface to generate photoelectrons. These electrons are passed through a magnetic field of $5 \times 10^{-4} \mathrm{~T}$. Assume that the radius of the largest circular path followed by these electrons is 7 mm, the work function of the
metal is :
(Mass of electron $=9.1 \times 10^{-31} \mathrm{~kg}$ )