The phenomenon of diffraction was discovered by ...... .

$A$ single slit of width $0.1\, mm$ is illuminated by a parallel beam of light of wavelength $6000\, \mathring{A}$ and diffraction bands are observed on a screen $0.5\, m$ from the slit. The distance of the third dark band from the central bright band is ........ $mm$.

$A$ single slit of width $d$ is illuminated by violet light of wavelength $400 \ nm$ and the width of the diffraction pattern is measured as $Y$. When half of the slit width is covered and illuminated by yellow light of wavelength $600 \ nm$,the width of the diffraction pattern is

Two slits are $1 \,mm$ apart and the screen is located $1 \,m$ away from the slits. $A$ light of wavelength $500 \,nm$ is used. The width of each slit to obtain $10$ maxima of the double slit pattern within the central maximum of the single slit pattern is $\ldots \ldots \ldots \times 10^{-4} \,m$.

$A$ slit of width $a$ is illuminated by monochromatic light of wavelength $650 \ nm$. The value of $a$ when the first maximum is formed at a diffraction angle of $30^\circ$ is:

In a single slit diffraction,the slit is illuminated with light of wavelength $6000 \text{ Å}$. If the slit were illuminated by a light of wavelength $\lambda$ the angular width of the central maximum decreases by $30 \%$. Then $\lambda$ is (in $\text{ Å}$)