The condition for diffraction is

$A$ single slit of width $0.1\, mm$ is illuminated by a parallel beam of light of wavelength $6000\, \mathring{A}$ and diffraction bands are observed on a screen $0.5\, m$ from the slit. The distance of the third dark band from the central bright band is ........ $mm$.

$A$ plane wavefront of wavelength $6 \times 10^{-7} \,m$ is incident on a slit of width $0.4 \,mm$. $A$ convex lens of focal length $0.8 \,m$ is placed behind the slit to form a diffraction pattern on a screen. What is the linear width of the second secondary maximum in $mm$?

The width of the $nth$ $HPZ$ (Half Period Zone) will be:

Which of the following waves exhibits clear diffraction?

$A$ slit of width $a$ is illuminated by monochromatic light of wavelength $650 \ nm$. The value of $a$ when the first maximum is formed at a diffraction angle of $30^\circ$ is: