What is quanta?

Photon is a quanta of light. Who introduced the concept of photon?

The phenomenon which suggested that light emitted in packets (quanta) is

The phenomenon which suggested that light emitted in packets (quanta) is

Photon is a quanta of light. Briefly explain the effect of intensity and energy of the incident radiation of the photo electric effect.

A certain day absorbs lights of lamda=400 nm and then fluorescence light of wavelength 500 mn. Assuming that under given condition 40% of the absorbed energy is re-emitted as fluorescence, calculate the ratio of quanta obserbed to number of quanta emitted out.