Consider two black bodies $A$ and $B$ having equal surface area. On the surface of $A, n$ photons of frequency $f$ are incident perpendicularly in a time $t$. On the surface of $B$, $2 n$ photons of frequency $3 f$ are incident perpendicularly in a time $4 t$. The ratio of average intensity of radiation on surface $A$ to that on surface $B$ is

A photon released by the transition of an electron from the second excited state to the ground state of Hydrogen atom is incident on the surface of a metal of work function 3.1 eV . The de-Broglie wavelength of the most energetic electron emitted from that metal surface is nearly

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