Question

Blue light falling on a double-slit produces interference fringes on a screen. What will happen to the fringes (closer together, farther apart, remain the same, or no more fringes) if The blue light is replaced by red light? The blue light is replaced by incoherent light? The separation between the slits is decreased? The distance to the screen is decreased? The entire experiment is immersed in water?

Answer 1

Fringe width is proportional to the wavelength of the light so in case of using red light instead of blue light the wavelength increases so the Fringe width will be increased.

If the source is not coherent then no interference will occur.

Fringe width is inversely proportional to the distance between the slits so if it decreases then Fringe width will increase.

Fringe width is proportional to the distance between the slits and the screen so if it gets decreased then Fringe width will also decreases

And if whole system is immersed in water then wavelength of the light is reduced so Fringe width will also decreases.