The photoelectric threshold wavelength of tungsten is $230\mathrm{nm}$. The energy of electrons ejected from its surface by ultraviolet light of wavelength $180\mathrm{nm}$ is

In an experiment on the photoelectric effect, the separation between the emitter and the collector plates is $10 \mathrm{cm}$. Plates are connected through an ammeter without any cell. A Magnetic field $B$ exists parallel to the plates. The work function of the emitter is $2.39 \mathrm{eV}$ and, the light of wavelengths between $400 \mathrm{nm}$ and $600 \mathrm{nm}$ is incident on it. If the minimum value of $B$ for which the current registered by the ammeter is zero is $n\times {10}^{–6} \mathrm{T}$. Then find out the value of $n$ (Neglect any effect of space charge). (Assume emission of photoelectron to be randomly every possible direction)