Question

Light passing through a double-slit arrangement is viewed on a distant screen. The interference pattern observed on the screen would have the widest spaced fringes for the case of:
blue light and a large slit spacing.
blue light and a small slit spacing.
red light and a small slit spacing.
red light and a large slit spacing.

Answer 1

The answer will be C.
The fringewidth \[\beta=\frac{ \lambda D }{ d }\]
Red has largest wavelength plus the spacing must be minimum to maximize the fringe width.