The de-Broglie wavelength of a particle moving with a speed of $0.8 c$ is equal to the wavelength of a photon. If $c$ is speed of the photon in vacuum, the ratio of the energy of the photon and the kinetic energy of the particle is

The additional energy that should be given to an electron to reduce its de-Broglie wavelength from 1 nm to 0.5 nm is

When monochromatic light falls on a photo sensitive metal, an electron is emitted with maximum velocity $1.6 \times 10^6 \mathrm{~m} / \mathrm{s}$. Find the stopping potential.

[charge of electron $=1.6 \times 10^{-19} \mathrm{C}$, mass of electron $\left.=9 \times 10^{-31} \mathrm{~kg}\right]$