Question

If the frequency of incident light is double, what will be the k.E. of the electrons emitted?

Answer 1

The energy of the photon used to reap the electron from the atom and give it some kinetic energy, thus -

hν=hcλ=12mv2+W0, where W0, the energy needed to reap the electron from the atom, is constant per type of atom. Thus v=2(hν−W0)m−−−−−−−√=2(hcλ−W0)m−−−−−−−√

As long as hν=hcλ>W0 - the electrons will be reaped from the metal. Changing frequency/wavelength of the photons won't change the number of reaped electrons, but will change their speed/kinetic energy.