Demonstrate that when light falls on a diffracting grating at right angles, the maximum resolving power of the grating cannot exceed the value `l//lambda`, where `l` is the width of the grating and `lambda` is the wavelength of light.

Explanation

Using
`R = (lambda)/(delta lambda) = kN = (Nd sin theta)/(lambda)`
`=(l sin theta)/(lambda) le (l)/(lambda)`.