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

$A$ light ray of wavelength $\lambda$ is passing through a pinhole of diameter $D$ and the effect is observed on a screen placed at a distance $L$ from the pinhole. The approximations of geometrical optics are applicable, if

In a single slit diffraction pattern, the distance between the plane of the slit and the screen is $1.4 \text{ m}$. The width of the slit is $0.66 \text{ mm}$. The second maximum is formed at the distance of $2.8 \text{ mm}$ from the center of the screen. The wavelength of light used is (in $\text{ Å}$)

$A$ narrow slit of width $2 \ mm$ is illuminated with a monochromatic light of wavelength $500 \ nm$. If the distance between the slit and the screen is $1 \ m$,then the first minima are separated by a distance of: (in $mm$)

Why does a $DVD$ store almost $30$ times more information than a $CD$?

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