If the slit width is $2 \, mm$ and the wavelength of light used is $4000 \, Å$, then the Fresnel distance is nearly:

The angular width of the central maxima in Fraunhofer diffraction for $\lambda = 6000 \; \mathring{A}$ is $\theta_{0}$. When the same slit is illuminated by another monochromatic light,the angular width decreases by $30 \%$. The wavelength of this light is ....... $\mathring{A}$.

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

In Fraunhofer diffraction,light of wavelength $6328 \ \mathring{A}$ is incident perpendicularly on a slit of width $0.2 \ mm$. The angular width of the secondary maxima or minima will be: (in $^{\circ}$)

In a Fresnel diffraction arrangement,the screen is at a distance of $2 \ m$ from a circular aperture. It is found that for light of wavelengths ${\lambda _1}$ and ${\lambda _2},$ the radius of the $4^{th}$ zone for ${\lambda _1}$ coincides with the radius of the $5^{th}$ zone for ${\lambda _2}.$ Then the ratio ${\lambda _1}:{\lambda _2}$ is

The diagrams below show the intensity distribution in diffraction of light of two sources. In which of the following cases the sources are just resolved?