Reflections: Light changes direction when it bounces off a surface.

Refraction: Light changes direction as it passes from one medium to another.

Example: when you see a pencil through water, the water changes the image of the pencil due to refraction.

• An example of refraction is when sunlight separates into a continuous spectrum when passed through a prism. Each color has a particular wavelength and each wavelength bends at a different angle. A prism separates light.

Diffraction: light changes direction when it passes through an opening or around obstacles

Interference: a phenomenon that occurs when two waves meet while traveling along the same medium.

Destructive:

Constrictive :

3 perplexing Experiments of the early 1900s:

• black body experiment

• photoelectric line emission spectra

• Hydrogen line

- These results could not be explained based on what was known then about light.

Maxwell Planck

Explained the blackbody experiment:

He concluded that light is emitted and absorbed by atoms in small quantities he called quanta.

We say energy is “quantized”