Question

In newton’s rings experiment, if we reduce the radius of curvature of planoconvex lens to zero, what will be effect on newton’s rings?

Answer 1

In Newton’s ring experiment, a plano-concave air film is formed between the glass slide and the convex lens. The formation of concentric circular fringes can be seen by interference. Irrespective of the nature of the lens ( whether plano or biconvex) for the same of radius of curvature, there will be no difference in the nature of the fringes. There may be a slight variation only in the intensity.

Answer 2

Answer:

In newton's rings experiment, if we reduce the radius of curvature of planoconvex lens to zero the fringes will be partially straight and are of equal thickness.

Explanation:

Fringes of equal thickness

• If the film is not plane parallel so that surface makes an appreciable angle with each other, the interfering ray do not enter the eye parallel to each other but appear to diverse from point near the film. The resulting films fringes appears be form in the film itself.
• If the fringes of equal thickness are produced in the air film between a convex surface of a long focal length and a plane glass surface the contour lines will be circular. These circular rings are called Newton's Ring.
• The diameter of the dark ring are

$D(n) = 4nRλ$

• where, D(n) = diameter of n th dark ring.
• n = number of rings
• R = radius of curvature of Plano-convex lens.
• If the two surfaces are plane so that the film is wedge shaped, the fringes will be partially straight following the line of equal thickness.
• If the radius of curvature of Plano-convex lens is zero, the circular fringes will not be formed instead partially straight fringes of equal thickness is formed.