Monochromatic light of wavelength 435 nm falls on a slit of width 0.095 mm. The slit is located 85 cm from a screen. How far is the center of the central bright band to the first dark band?

Answer 1

when the ray from the edge of the slit hits with the ray from the middle travels half a wavelength shorter you get a dark spot.
(width /2) sin angle = wavelength / 2
for small angles sin angle = angle = y / distance to screen
so
y = distance to screen * wavelength / width of slot
= 0.85 * 435*10^-9 / 95*10^-6