Write three characteristic features in photoelectric effect that cannot be explained on the basis of wave theory of light, but can be explained only using Einstein's equation.

The three characteristics of photoelectric effect, which cannot be explained on the basis of wave theory of light are: 

1. For a given metal and frequency of incident radiation, the number of photoelectrons ejected per second is directly proportional to the intensity of the incident light. 

2. For a given metal, a certain minimum frequency of the incident radiation below which no emission of photoelectrons take place. The is the threshold frequency. 

3. Above the threshold frequency, the maximum kinetic energy of the emitted photoelectron is independent of the intensity of the incident light and is dependent only upon the frequency or wavelength of the incident light.