Q. Give basic postulate of special theory of relativity?
A plane-convex lenses L of large radius of curvature with its convexities is placed on a plane glass plate P. When light from an extended monochromatic source is allowed to fall on plane glass plate G inclined at an angle of 45 degree to the incident beam, it reflects incident light beam in vertically downward direction on the system (Plano-convex lens L + Plane glass plate P). The light waves reflected form the top and bottom surfaces of the air film produces interference fringes. These interference fringes (rings) may be seen by using a low power microscope.
Theory: The phenomenon of the formation of the Newton's rings can be explained on the basis of wave theory of light. When a light ray iP1 from an extended monochromatic light source S is allowed to fall normally on the system (Plano-convex lenses L+ Plane glass plate P), it gets partially reflected a long P1R1 at point P1 and partially transmitted along the path P1P2 and again reflected by upper surface of glass plate along P2R2 at point P2.
There is no phase change at the lens-air surface i.e. at point P1, because the light ray is going from a medium of higher refractive index to lower refractive index.