What is light?
Light is electromagnetic radiation, particularly radiation of a wavelength that is visible to the human eye. In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether it is visible or not.
In the seventeenth and eighteenth centuries, scientist debated about lights, did light travel as particle or as a wave.
Light as a particle
Albert Einstein showed by imagining photoelectric effect, when light interacts with an object, it forms a particle.
Light as a wave
Thomas Young formed an experiment called double-slit experiment.
Single beam of laser light passes through the slits, then it’s diffracted so it spreads to the screen.
In double slit experiment, we determine λ using this equation
a, is the separation of the slits
x, is the distance between the centers of the fringes
D, is the distance between slits to the screen