Question

write the significance of planck's proposal?

Answer 1

plank.s law describ the spectral density of electromagnet radation emitted by blank body in thermal equilibrium at given temperture

Answer 2

I assume that you are referring to Planck's constant by saying planck's proposal. 

Planck's constant denotes the relationship between energey within one quantum/photon of electromagnetic radiation to the frequency of corresponding radiation. It is denoted by 'h'.

It is important concept in quantum physics as it describes the behavior of particles and waves on a smallest atomic scale.

Equation of planck's constant is, E=hv, where E is the energy and v is the frequency of the radiation. Simplest practical example of use of planck's constant is, let's assume that you are shining a bright color light of frequency of xx hertz on a surface of metal, which causes electron to be emitted. and if we want to calculate the energy that is emitted by each photon, we can use the E=hv.