Question

$n$ th bright fringe if red light $\left(\lambda_{1}=7500\, \mathring{A}\right.$ ) coincides with $(n+1)$ th bright fringe of green light $\left(\lambda_{2}=6000\, \mathring{A}\right)$. The value of $n$, is

• A. 4
• B. 5
• C. 3
• D. 2

Answer 1

Answer: (A)

As the two bright fringes coincide
$\therefore n \lambda_{1}=(n+1) \lambda_{2}$
$\frac{n +1}{n}=\frac{\lambda_{1}}{\lambda_{2}}$
$=\frac{7500}{6000}=\frac{5}{4}$
$1+\frac{1}{n}=\frac{5}{4} $
$\Rightarrow n=4$