Question:
In an experiment on photoelectric effect, the emitter and the collector plates are placed at a separation of $10 \mathrm{~cm}$ and 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 incident on it has wavelengths between $400 \mathrm{~nm}$ and $600 \mathrm{~nm}$. Find the minimum value of B for which the current registered by the ammeter is zero. Neglect any effect of space charge.
Figure 42-E3
Solution:
