The work function of a metal is

Ultraviolet light of wavelength $300 \ nm$ and intensity $1.0 \ watt/m^2$ falls on the surface of a photosensitive material. If $1\%$ of the incident photons produce photoelectrons, then the number of photoelectrons emitted from an area of $1.0\  cm^2$ of the surface is nearly

Rest mass energy of an electron is $0.51\  MeV.$ If this electron is moving with a velocity $0.8\ c$ (where $c$ is velocity of light in vacuum), then kinetic energy of the electron should be. ……….. $MeV$

Monochromatic light of frequency $6.0 \times 10^{14}\,\, Hz$ is produced by a laser. The power emitted is $2 \times 10^{-3}\,\, W.$ The number of photons emitted, on the average, by the source per second is

Energy of a quanta of frequency ${10^{15}}Hz$ and $h = 6.6 \times {10^{ – 34}}J{\rm{ – }}\sec $ will be