A. describe the photoelectric effect and explain why it could not be explained by newtonian physics.

b. explain what is meant by quantized light, and discuss why the photoelectric effect provides evidence for it.

c. write 2 - 3 sentences explaining how quantum mechanics describes light and matter. how do the distinct lines in the emission spectra of elements support the idea that light can behave as a particle?

Explanation:

(a)

The photoelectric effect is the phenomenon in which the light of the particular frequency incidents on the material. Then the emission of the electrons from the surface of the material occurs.

This phenomenon could not be explained by Newtonian physics.

In Newtonian physics, the energy is not discrete. In quantum mechanics, the energy is discrete.  This is the main why the photoelectric effect could not be explained by Newtonian physics.

(b)

Light consists of  photons. The photon is a packet of energy. It is also called quanta. The energies of the photons are quantized.  

When a photon strikes on the surface of metal then the energy of photon is absorbed by an electron in the metal so that it may eject from the surface. This phenomenon is called the photoelectric effect.

(c)

In quantum mechanics, wave-particle duality concept is used to explain the wave-particle nature of the light. Light behaves as particle as well as wave. It shows both nature. The photoelectric phenomenon shows the particle nature of the light. It acts as a particle when it hits the surface of the metal.

In line spectra, the electron is excited to an energy level. In this case energy is transferred from photon to electron. There is a collision between photon and electron. The change in momentum will occur. It shows the particle nature of the light.  

one "light year" is the distance that light travels, through vacuum, in one julian year.   that's 365.25 days, of 24 hours each.