In Fresnel diffraction,if the distance between the disc and the screen is decreased,the intensity of the central bright spot will

Fraunhofer lines are produced by

The direction of the first secondary maximum in the Fraunhofer diffraction pattern at a single slit is given by ($a$ is the width of the slit):

In a Fraunhofer diffraction pattern,the slit width is $0.2 \ mm$ and the screen is at $2 \ m$ away from the lens. If the distance between the first minimum on either side of the central maximum is $1 \ cm$,the wavelength of light used is: (in $Å$)

In a Fraunhofer diffraction of a single slit, when a slit is illuminated by a light of wavelength $6480 \text{ Å}$, the angular width of the central maximum is measured. When the slit is illuminated by light of another wavelength '$\lambda$',the angular width decreases by $25\%$. The value of '$\lambda$' in $\text{Å}$ is:

Fresnel diffraction is produced due to light rays falling on a small obstacle. The intensity of light at a point on a screen beyond an obstacle depends on