$A$ slit of width $a$ is illuminated by red light of wavelength $6500 \, \mathring{A}$. The first minimum will fall at $\theta = 30^{\circ}$ if $a$ is equal to:

Assertion : When a tiny circular obstacle is placed in the path of light from some distance,a bright spot is seen at the centre of the shadow of the obstacle.
Reason : Destructive interference occurs at the centre of the shadow.

$A$ screen is placed $0.5 \,m$ away from a single slit which is illuminated by a monochromatic light of wavelength $6000 \text{ Å}$. If the distance between the first and third minima in the diffraction pattern on the screen is $3 \,mm$, then the slit width is: (in $\,mm$)

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

In a single-slit diffraction pattern,if the source of light is replaced by a source of shorter wavelength,the width of the central maximum will:

In an experiment,electrons are passed through a narrow slit of width $d$ equal to their de Broglie wavelength. They are detected on a screen at a distance $D$ from the slit. Which of the following graphs represents the number of electrons $N$ detected as a function of the detector position $y$ ($y = 0$ corresponds to the middle of the slit)?