The work done to accelerate an electron from rest so that it can have a de-Broglie wavelength of $6600 \mathop {\rm{A}}\limits^{\rm{o}}$ is nearly

(Planck's constant $=6.6 \times 10^{-34} \mathrm{Js}$ and mass of electron $=9 \times 10^{-31} \mathrm{~kg}$ )

When photons incident on a photosensitive material of work function 1.5 eV , the maximum velocity of the emitted photoelectrons is $8 \times 10^5 \mathrm{~ms}^{-1}$. The stopping potential of the photoelectrons is

(Mass of the electron $=9 \times 10^{-31} \mathrm{~kg}$ and charge of the electron $=1.6 \times 10^{-19} \mathrm{C}$ )

20 kV electrons can produce X- rays with a minimum wavelength of

When a photosensitive material is illuminated by photons of energy 3.1 eV , the stopping potential of the photoelectrons is 1.7 V . When the same photosensitive material is illuminated by photons of energy 2.5 eV , the stopping potential of the photoelectrons is