Question

Why is monochromatic light used in Newton’s ring?

Answer 1

Newton's rings are a phenomenon that occurs when light is reflected between two surfaces: a spherical surface and an adjacent touching flat surface. It was named after Isaac Newton, who studied the effect in$1666$.

Complete step-by-step solution:
Newton's rings appear as a series of concentric, alternating bright and dark rings centered at the point of contact between the two surfaces when viewed in monochromatic light. Because the different wavelengths of light interfere at different thicknesses of the air layer between the surfaces, it forms a concentric ring pattern of rainbow colors when viewed with white light.
Lights are made up of a variety of colors. Sunlight is made up of seven different colors. The term monochromatic refers to the use of only one color. Monochromatic light is defined as any light that is pure of a single color. Although technically it only has a single wavelength, no real electromagnetic radiation is purely monochromatic, so monochromatic light is said to have a wavelength within a very short wavelength range.
A monochromatic source is a light source that emits only one color of the light (flash units are monochromatic, usually$5000K$). Simply put, light with the same wavelength will only show a single color and will be monochromatic.
When using monochromatic light, the interference pattern is visible. Because different wavelengths of light interfere at different thicknesses when white light is used, the interference pattern is not very clear.
Note: Two plano-convex lenses with flat surfaces in contact show Newton's rings. The rings are formed by one slightly convex surface. Because the different wavelengths of each color interfere at different locations, the rings appear rainbow-colored in white light.