Defining Light

Light has "duality" concept, travel in the form of waves when radiate, and in the form of particles when interact with matter.

Thomas Young's slit experiment confirmed that light travel as waves. The requirements are:

• 2 sets of waves
• both have same wavelength
• The phase difference must be constant

The interference caused from 2 slits overlapping diffracted beams.

Constructive interference make a bright fring, and destructive interference make a dark fringe.

Wavelength or λ can be determined by using this formula: 

Slit separation a, distance between the centers or edges of slits

Fringe separation x, distance between centers of adjacent bright or dark fringes

slit-to-screen distance D, distance from midpoint of the slits to the central fringe on the screen