Two identical photo cathodes receive light of frequencies mathrm{f}_{1} and mathrm{f}_{2}. the velocities of the photoelectrons (of mass 'm') coming out are respectively mathrm{v}_{1} and mathrm{v}_{2}, then:displaystyle mathrm{v}_{1}^{2}-mathrm{v}_{2}^{2}=frac{2mathrm{h}}{mathrm{m}}(mathrm{f}_{1}-mathrm{f}_{2})displaystyle mathrm{v}_{1}+mathrm{v}_{2}=[frac{2mathrm{h}}{mathrm{m}}(mathrm{f}_{1}+mathrm{f}_{2})]^{1/2}displaystyle mathrm{v}_{1}^{2}+mathrm{v}_{2}^{2}=frac{2mathrm{h}}{mathrm{m}}(mathrm{f}_{1}+mathrm{f}_{2})displaystyle mathrm{v}_{1}-mathrm{v}_{2}=[frac{2mathrm{h}}{mathrm{m}}(mathrm{f}_{1}-mathrm{f}