When white light is incident on a grating the central maximum is white. Spectra are produced at the other order maxima.
Consider the grating relationship:
for any particular grating \(d\) is constant
for each order maximum \(n\) is the same
Therefore:
\(\sin \theta\) depends only on wavelength
Hence the bigger the wavelength the bigger the angle \(\theta\)
Question
If the brightness of light in a double slit experiment is increased what happens to the fringe spacing (distance between two consecutive maxima or minima)?
There is no change in fringe spacing - this only depends on the wavelength and slit spacing.
If the wavelength of light increases (eg red instead of blue light) the fringe spacing would increase.