$A$ screen is placed $0.5 \,m$ away from a single slit which is illuminated by a monochromatic light of wavelength $6000 \text{ Å}$. If the distance between the first and third minima in the diffraction pattern on the screen is $3 \,mm$, then the slit width is: (in $\,mm$)

$A$ slit of width $a$ is illuminated by light of wavelength $\lambda$. The linear separation between $1^{st}$ and $3^{rd}$ minima in the diffraction pattern produced on a screen placed at a distance $D$ from the slit system is . . . . . . .

Through a narrow slit of width $2 \,mm$, a diffraction pattern is formed on a screen kept at a distance $2 \,m$ from the slit. The wavelength of the light used is $6330 \mathring{A}$ and it falls normal to the slit and screen. Then, the distance between the two minima on either side of the central maximum is (in $\,mm$)

$A$ wavefront presents one,two and three $HPZ$ at points $A, B$ and $C$ respectively. If the ratio of consecutive amplitudes of $HPZ$ is $4 : 3$,then the ratio of resultant intensities at these points will be

For a parallel beam of monochromatic light of wavelength $\lambda$,diffraction is produced by a single slit whose width $a$ is of the order of the wavelength of the light. If $D$ is the distance of the screen from the slit,the width of the central maxima will be

The penetration of light into the region of geometrical shadow is called: