If the electron in hydrogen atom jumps from second Bohr orbit to ground state and difference between energies of the two states is radiated in the form of photons. If the work function of the material is $4.2\mathrm{eV}$  then stopping potential.[Energy of electron in $n^{\text{th }}$ orbit $\left.=-\frac{13.6}{n^2}\mathrm{eV}\right]$

A beam of monochromatic light of wavelength $\lambda$ ejects photoelectrons from a caesium surface $\left({\mathrm{W}}_0=1.9 \mathrm{eV}\right)$ which are made to collide with hydrogen atoms in ground state. The maximum value of $\lambda$ for which hydrogen atoms may be ionised is

(Take value of $h=6.6\times {10}^{-34}$ in SI units)

A point sources of light is used in a photoelectric effect. If the sources is removed farther from the emitting metal, the stopping potential 

The following graph represents the variation of photo current with anode potential for a metal surface. Here $I_1, I_2$ and $I_3$ represents intensities and ${\gamma }_1,{\gamma }_2,{\gamma }_3$ represents frequency for curves $1, 2$ and $3$ respectively, then