Diffraction of light occurs only when the dimension of the obstacle is .....

In a single slit diffraction pattern:

Light of wavelength $5000 \, \mathring{A}$ is incident on a single slit such that the first minima is formed at a distance $5 \, mm$ from the centre. If the screen is placed $2 \, m$ away,then find the width of the slit in $mm$.

$A$ 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:

In a diffraction pattern due to a single slit,the angular width of the central maxima becomes half when the wavelength of the light used is changed from $\lambda$ to $7000 Å$. Then the value of $\lambda$ is (in $Å$)

At the first minimum adjacent to the central maximum of a single-slit diffraction pattern,the phase difference between the Huygens' wavelet from the edge of the slit and the wavelet from the midpoint of the slit is