In Young's double slit experiment for what order does the wavelength of red light $(\lambda=780 \mathrm{~nm})$ coincide with $(n+1)$ th order of blue light $(\lambda=520 \mathrm{~nm})$ ?

The angular width of a fringe in a double slit experiment is found to be $0.2^{\circ}$ on a screen 1 m away the wavelength of light used is 600 nm . The change in angular width of the fringe, if the entire measurement system is immersed in water is [use refractive index of water as $4 / 3$ ]

A Young's double slit experiment apparatus has slits separated by 0.2 mm and a screen 60 cm away from the slits. The whole apparatus is immersed in a liquid medium of refractive index $11 / 9$ and the slits are illuminated with green light ( $\lambda=550$ nm in vacuum). Find the fringe width of the pattern formed on the screen.

If in a Young's double slit experiment the slit separation is doubled and the distance of the screen from the slits is reduced to half, then the fringe widths become how many times their original value?