Question

In Youngs experiment, the wavelength of red light is $7800\, ?$ and that of blue light is $5200\, ?$. The value of n for which $(n+1)th$ blue band coincides with nth red band is

• A. 1
• B. 2
• C. 3
• D. 4

Answer 1

Answer: (B)

2

Answer 2

For coincidence of bands or $\frac{n D \lambda_{1}}{d} =\frac{(n+1) D \lambda_{2}}{d}$ or $n \lambda_{1} =(n+1) \lambda_{2}$ $7800 n =5200(n+1)$ or $n =2$