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 $\left.=9 \times 10^{-31} \mathrm{~kg}\right]$

A lamp of power 942 W radiates energy uniformly in all direction. The wavelength of radiation is 660 nm .The photon flux on a small screen 5.0 m from the lamp in units of photon $/ \mathrm{m}^2 \mathrm{~s} Q$ is

(take Planck's constant, $h=6.6 \times 10^{-34}$ SI unit)