$A$ 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:

Light of wavelength $5000 \, \text{Å}$ is incident on a slit of width $0.1 \, \text{mm}$. Find the width of the central bright fringe on a screen placed at a distance of $2 \, \text{m}$ in $\text{mm}$.

$A$ diffraction pattern is obtained by using a beam of red light. If the red light is replaced by blue light,then:

$A$ circular disc is placed in front of a narrow source. When the point of observation is at a distance of $1 \, m$ from the disc,the disc covers the first $HPZ$ (Half Period Zone). The intensity at this point is $I_0$. The intensity at a point at a distance of $25 \, cm$ from the disc will be:

The luminous border that surrounds the profile of a mountain just before the sun rises behind it is an example of:

In a single slit diffraction of light of wavelength $\lambda$ by a slit of width $e$,the size of the central maximum on a screen at a distance $b$ is