Wave theory of light considers only the wave nature of radiation and not the particle nature.Various phenomena like interference,diffraction are successfully explained by it.But Black-body radiation,photoelectric effect etc. can’t be explained.
 An ideal body which is perfect absorber and perfect emitter is called as black-body.When such a body is heated it becomes red,further increase in temperature,the colour changes from red to yellow then to white and finally purple as the T becomes very high.This shows that wavelength of radiation emitted by black-body decreases with increase in T and frequency of radiation emitted increase with T.But according to electromagnetic wave theory,the power is emitted or absorbed continuously.Thus,the power of any electromagnetic radiation is proportional to its intensity,i.e.square of amplitude and is independent of its frequency or wavelength.So,according to the wave assumption,the radiation emitted by the body being heated should have the same color,although its intensity may vary as the heating is continued.