For the visibility of a diffraction pattern of a wave of light,the size of the slit or obstacle should be

$A$ slit of width $a$ is illuminated by red light of wavelength $6500 Å$. If the first diffraction minimum falls at $30^{\circ}$,then the value of $a$ is

$A$ single slit diffraction pattern is formed with white light. For what wavelength of light the $4^{\text{th}}$ secondary maximum in the diffraction pattern coincides with the $3^{\text{rd}}$ secondary maximum in the pattern of light of wavelength $\lambda$?

Light of wavelength $\lambda$ is incident on a single slit of width $a$ and the distance between the slit and the screen is $D$. In the diffraction pattern, if the slit width is equal to the width of the central maximum, then $D$ is equal to:

$A$ screen is placed at a certain distance from a narrow slit,which is illuminated by a parallel beam of monochromatic light. What will you observe if you scan the screen with the help of a microscope?

To observe diffraction,the size of the obstacle