(Solved): A Light from a point source 10cm away from a converging lens passes through the lens and converge ...

A Light from a point source $10\mathrm{cm}$ away from a converging lens passes through the lens and converges again $10\mathrm{cm}$ away from the lens on the other side to form an image. What is the focal length of the lens? $\begin{array}{l}\frac{1}{10\mathrm{cm}}+\frac{1}{10\mathrm{cm}}=\frac{1}{f}\\ \mathrm{f}=5.0\mathrm{cm}\end{array}$ stopping potential that prevents electrons from flowing across a certain photocell is $4.0\mathrm{V}$. What inetic energy given to the electrons by the incident light? (answer in both $J$ ) $\mathrm{KE}=?{\mathrm{qV}}_0$ $ke=?V_0$