YDSE Problems II

Q. In Young's double slit interference experiment the wavelength of light used is 6000A. If the path difference between waves reaching a ponit P on the screen is 1.5 microns, then at that point P:

1. second bright band occurs
2. second dark band occurs
3. third dark band occurs
4. thirdbright band occurs

Q.

White light is used to illuminate the two slits in Young's double slit experiment. The distance between the slits is b and the screen is at a distance d (>> b) from the slits. At a point on the screen directly in front of one of the slits, certain wavelengths are missing. Some of these missing wavelengths are

1. $\lambda =\frac{b^2}{2d}$

2. $\lambda =\frac{2b^2}{d}$

3. $\lambda =\frac{b^2}{3d}$

4. $\lambda =\frac{2b^2}{3d}$

Q. In an interference pattern the $(n+4{)}^{th}$ blue bright fringe and $n^{th}$ red bright fringe are formed at the same spot. If red and blue light have the wavelength of $7800\AA$ and $5200\AA$, then value of $n$ should be :