Question

In an interference pattern of a point we observe 16^th bright fringe for l₁ = 6000 Å. What order will be visible if the source is replaced by another bright fringe l₂ = 4800 Å?

• A. 12
• B. 20
• C. 18
• D. 24

Answer 1

Answer: (B)

20

Answer 2

The distance of a bright fringe from zero order fringe is given by x_n =$\frac{n\lambda D}{2d}$

Then at a given point n l is constant n₁l₁ = n₂l₂

n₂ =$\frac{n_{1}\lambda_{1}}{\lambda_{2}}$=$\frac{16 \times 6000}{4800}$= 20