Question

In Young's double slit experiment, the wavelength of red light $7500\stackrel{\circ }{A}$ and that of blue light is $5000\stackrel{\circ }{A}$. The value of $n$ for which $n^{th}$ bright band due to red light coincides with $(n+1{)}^{th}$ bright band due to blue light, is

• A. $1$
• B. $2$
• C. $3$
• D. $4$

Answer 1

The correct option is B $2$

For bright

distance $y=n\lambda \frac{D}{d}\therefore n=7500\frac{D}{d}=(n+1)5000\frac{D}{d}\therefore \frac{n}{n+1}=\frac{2}{3}\therefore n=2$