Q. In Newton's ring experiment, the diameter of certain order of dark ring is measured to be double that of the second ring. What is the order of the ring?
Data : dn = 2d2 ; n = ?
dn2 = 4nRλ
d22 = 8Rλ
dn2 / d22 = n / 2
( 4d22 / d22 ) / ( n / 2)
∴ n = 8.