Mercury violet light (λ=4558 ∘A) is falling on a photosensitive material (ϕ=2.5 eV). The speed of the ejected electrons is in ms−1, about
2.65×105
By using E=W0+12mv2max; where E=123754558=2.71 eV
⇒2.71 eV=2.5 eV+12×9.1×10−31×v2max
⇒0.21×1.6×10−19=12×9.1×10−31×v2max
⇒vmax=2.65×105 m/s