Due to which optical phenomenon do we not see the shadow of an opaque object clearly?

When the distance of separation between the slit and screen is doubled, the angular separation between fringes in single slit diffraction pattern experiment

If $\lambda = 6000 \, \mathring{A}$ and $a = 18 \times 10^{-5} \, \text{cm}$,find the angular width of the central maximum in degrees $(^\circ)$.

The condition for observing Fraunhofer diffraction from a single slit is that the light wavefront incident on the slit should be

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 $\text{ Å}$)

Two slits are made $1 \; mm$ apart and the screen is placed $1 \; m$ away. What should the width of each slit be to obtain $10$ maxima of the double-slit pattern within the central maximum of the single-slit pattern (in $; mm$)? Blue-green light of wavelength $500 \; nm$ is used.