viva questions on newtons rings

1.) What are Newton rings ?
Ans.) Dark and bright rings ar formed due to the presence of air film when Plano convex lens is placed on glass plate .

2.) How are Newton's rings formed ?
Ans.) They are formed due to the result of interface between light wave reflected from upper and lower surface of the air film developed between the convex surface of Plano convex lens and Plano glass plate .
3.) What is the function of 45 inclined glass plane in experiment setup ?
Ans.) It turns the light Ray coming from an external source to 90° and so the Ray fall normal on the Plano convex lens .
4.) Why rings get closer as their order increase ?
Ans.) The diameter of the dark frings is directly proportional to the square root of natural numbers .while bright rings are directly proportional to the square root of odd numbers .hence they don't increase at the same rate .
5.) What happens if we us plane glass in experiment setup instead of convex lens ?ans.) The shape of rings will be irregular if we use plane glass .so this may result in finding exact measurements .so to overcome this problem we use convex lens .
6.) What happens to size of rings if we use lens of small radius of curvature ?
Ans.) The rings will form with a small radius of curvature if we lens of small radius of curvature .
7.) What happens if we use white light instead of sodium light Ray ?
Ans.) If we use white light instead of sodium light few colored will be observed near center .
8.)Wh happens if we introduce water in between the lens and glass ?
Ans.) Diameter of rings will decrease if we introduce water between the lens and glass .as it is inversely proportional to refractive index .
9.)What process takes place during the formation of Newton rings ?
Ans.) Interference,reflection.
10.) What  is the formula for Newton ring ?
Ans.) (Dm)2-(dn)2/(n-m)R
11.) What are the equipments used during the experiment ?
Ans.)Travelling microscope,a sodium lamp,newtons ring apparatus,a spherometer, a cone lens of short focal length .
12.) Why Newton rings are circular in shape?
Ans.) The air film formed is wedge shaped locus of point of intersection is equal to the thickness of circles .
13.)  What are the uses of Newton's ring experiment ?
Ans.) Quality control of optical surface,we can also find the  wavelenght of any light Ray,refractive index of the liquid.
14.) why sometimes rings are not in circuar shape reason ?
ans.)(i) if the plate is not  optically flat.
(ii) when the surface of the lens is not be the part of a perfect sphere;
(iii) if the plate,lens are not cleaned perfectly.
15.)on what factors the radius of the ring depends on ?
Ans.)The radius of rings mainly depends  on the following factors :
(i) wavelength of light used.
(ii) refractive index  of enclosed film.
(iii) radius of curvature R of convex lens.

16.)Why is the centre of the ring dark?
Ans. At centre, the thickness of air film is zero . but at the point of contact the
two interfering rays are opposite in phase and produce zero intensity.
17.) what is meant by interferece ?
Ans.) in physics interference is defined as the combination of two or more electromagnetic waves to form a resultant wave .
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