Write the condition of $n^{th}$ order maximum in diffraction.

The position of the direct image obtained at $O$,when a monochromatic beam of light is passed through a plane transmission grating at normal incidence,is shown in the figure. The diffracted images $A, B$,and $C$ correspond to the first,second,and third-order diffraction. When the source is replaced by another source of shorter wavelength,then:

In deriving the single slit diffraction pattern,it is stated that the intensity is zero at angles of $\theta = n\lambda / a$,where $a$ is the slit width. Justify this by suitably dividing the slit to bring out the cancellation.

$A$ 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 experiment,when the distance of separation between the slit and the screen is doubled,the angular separation between the fringes

In a single slit diffraction experiment, the first minimum for red light $(660 \ nm)$ coincides with the first secondary maximum of some other wavelength $\lambda$. The value of $\lambda$ is $..... \mathring{A}$.