# Introduction to Interference and Diffraction

Light exhibits both the properties of a wave and a particle. Its wave-like properties are best shown in its propagation while the particle-like properties in the emission and absorption of light.[1] As light behaves like a wave, superposition is observed between interacting waves. Superposition of waves is the addition of waves that travel across the same medium. The resulting wave from this addition has amplitude at a particular point that is the algebraic sum of the amplitudes of its constituent waves.[3] This superposition of waves can be observed as interference and diffraction when light passes through apertures or obstacles.

When light breaks up as it passes through an aperture or an obstacle, a diffraction pattern is observed. The regions in the pattern where light is visible are called the maxima. On the other hand, the regions where light is invisible are called the minima. In a slit and screen setup, a relationship between the slit width (α), order of the minimum (m), wavelength of the incident light (λ), distance from the center of the pattern to a minimum (y1), and distance from the slit to the screen (D) can be written as: α=mλDy1 m is a positive integer (equation 1)

This equation is derived from the relation a sinθ=mλ and with the use of trigonometry and small angle approximation, the assumption sinθ≈tanθ=y1/D has been made. By substituting the latter to the first relation and manipulating the equation to isolate the slit width to the left hand side of the equation, we arrive with equation 1.

Methodology

A diode laser was placed on one end of an optical bench and a white paper that acts as a screen is placed on the other end. The white paper could be replaced with a light-sensitive material that would leave markings when struck by a beam of light. This is to prevent human error in marking the diffraction pattern. A single slit disk in its holder was placed between the laser and the screen facing the laser and about...

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