Question

in a Newton's ring experiment the diameter of 5th dark ring is reduced to half of its value after placing a liquid between plane glass and convex surface calculate the refractive index of liquid​

Answer 1

I HAVE CALCULATED 20TH RING

Answer 2

Answer:

Explanation:

Theory: According to the theory, circular rings are formed due to interference of light rays reflected from

the upper and lower surfaces of the air film formed between the convex surfaces of plano convex lens and

plane glass plate. The incident ray is divided into two coherent rays by reflection from the upper and

lower surfaces of the wedge shaped air film. The reflected rays interfere and produce bright and dark

circular rings around the point of contact.

Newton’s ring for reflected light the path difference between two rays is given by

∆= 2µt cos (r + θ) + λ/2

For normal incidence and air film i=0, r= 0, µ= 1 and θ is very small hence cosθ is very small. Hence

path difference become ∆= 2µt + λ/2

Diameter of ring:

The diameter of dark fringe is directly proportional to square root of natural number (n).

Dn = √4n λR.

Seen the upper surface of wedge shaped film form in Newton’s ring experiment is not plane, the diameter

and also the width of rings are not increasing constantly.PROCEDURE :

1. Find out the least count of traveling microscope using formula.

2. Observe Newton’s rings(circular dark and bright rings ) by means of traveling

microscope.

3. Adjust the position of the microscope till the point of intersection of cross-wire

coincides with the center of ring pattern.

4. Shift the traveling microscope to the left side till the vertical cross-wire become

tangential at the center of the 12

th dark ring.

5. Note the traveling microscope reading i.e. main scale reading (M.S.R.) and

Vernier scale reading (V.S.R.) as given in the format.

6. Shift the microscope in the reverse direction till the vertical cross-wire becomes

tangential to the 10th, 8th, 6th, 4th, 2nd dark ring and note down M.S.R. and V.S.R.

every time.

7. Rotate the traveling microscope screw in the same direction, cross over the center

of the rings and note down the M.S.R. and V.S.R. readings for 2nd, 4th, 6th, 8th and

10th dark ring to the right side.

8. Transfer the final readings from observation table A to observation table B and

compete the calculations.

9. Plot a graph of the square of the diameter (D2

n) Vs number of rings (n).

10. Calculate the radius of curvature of the plano-convex lens (R) from slope of the

graph.