Red light of wavelength `6500 Å` from a distant source falls on a slit `0.50 mm` wide. Calculate the distance between first two dark bands on each side of central bright band in the diffraction pattern observed on a screen placed `1.8 m` from the slit.

Explanation

Given `lamda=6500Å=65xx10^(-8)m,a=0.5mm=0.5xx10^(-3)m,D=1.8m`
Required distance between two dark bands will be equal to width of central maxima.
`W_(A)=(2lamdaD)/(a)=(2xx6500xx10^(-10)xx18)/(0.5xx10^(-3))=468xx10^(-5)m=4.68mm`