A light beam of wavelength 500 nm is incident on a metal having work function of 1.25 eV, placed in a magnetic field of intensity B. The electrons…

A light beam of wavelength $\displaystyle 500$ nm is incident on a metal having work function of $\displaystyle 1.25$ eV, placed in a magnetic field of intensity $\displaystyle B$. The electrons emitted perpendicular to the magnetic field B , with maximum kinetic energy are bent into circular arc of radius $\displaystyle 30$ cm . The value of B is \_\_\_\_ $\displaystyle \times 10^{-7} \mathrm{~T}$. Given $\displaystyle \mathrm{hc}=20 \times 10^{-26} \mathrm{~J}-\mathrm{m}$, mass of electron $\displaystyle =9 \times 10^{-31} \mathrm{~kg}$