What is photoelectron ? 

A point source of light is placed at the centre of curvature of a hemispherical surface. The source emits a power of $24\,W$ The radius of curvature of hemisphere is $10\,cm$ and the inner surface is completely reflecting. The force on the hemisphere due to the light falling on it is $..........\times 10^{-8}\,N$.

There are materials which absorb photons of shorter wavelength and emit photons of longer wavelength. Can there be stable substances which absorb photons of larger wavelength and emit light of shorter wavelength. 

Light of wavelength $5000\,\,\mathop A\limits^o $ falling on a sensitive surface. If the surface has received $10^{-7}\,J$ of energy, then the number of photons falling on the surface will be

According to Einstein's photoelectric equation, the graph between the kinetic energy of photoelectrons ejected and the frequency of incident radiation is

In photoelectric effect, the electrons are ejected from metals if the incident light has a certain minimum