Why fringes are circular in newtons ring

Hence the fringes are circular in shape. To calculate the diameter of fringes, assume a plano-convex lens is placed on a plane glass plate as shown in figure say R be the radius of curvature of lens. The diameter of n th order dark fringe will be.

The diameter of n th order bright fringe will be. The diameter of bright ring is proportional to square root of odd natural numbers. For example the diameter of dark ring is given by. If the monochromatic source is replaced by the white light few coloured rings are seen around dark centre later illumination is seen in the field of view. Class Attendance. Important Questions. MST-I Result. Exam Schedule. MST-I Nov Amita Mourya. Engineering Physics by Dr. Amita Maurya, Peoples University, Bhopal.

Formation of fringes When a plano-convex lens with large radius of curvature is placed on a plane glass plate such that its curved surface faces the glass plate, a wedge air film of gradually increasing thickness is formed between the lens and the glass plate.

The thickness of the film is constant over a circle or concentric circles having center at the center of the lens. Hence the fringes are circular. It is named after Isaac Newton, who investigated the effect in It is named after great scientist Isaac Newton who investigated the effect in his treatise Opticks in It is also possible that the spacing between rings is too small to see comfortably if the spacing between the lens and glass plate varies too fast.

But you can arrange to see them with naked eye. Actually you can see a similar pattern between two microscope slides pressed together. Hence, at the geometrical path difference between the incident and reflected rays from the glass plate is zero. This path difference gives destructive interference at the centre, and hence the centre is dark. Here we neglect laser frequency fluctuations and refractive-index variations.