Question

In Newtons’s ring experiment,what will be the order of dark ring which will have double the diameter of 40th dark ring? 

Answer 1

For dark ring 

`D_n^2 = 4  n  λ  R`

`D_40^2 = 4 × 40 × λ × R …………(1)`

Let n^th be the order of ring whose diameter is double the diameter of 40^th dark ring . 

`(2D_40)^2 = 4 × n × λ × R…………….(2)`

From equation 1 and 2

`(D_40^2)/(4D_40^2) = 40/ n`

n= 160 

Value of n = 160