(a) In a diffraction experiment, the slit is illuminated by light of wavelength 600 nm . The first minimum of the pattern falls at $\theta=30^{\circ}$. Calculate the width of the slit.

OR

(b) In a Young's double-slit experiment, two light waves, each of intensity $I_0$, interfere at a point, having a path difference $\frac{\lambda}{8}$ on the screen. Find the intensity at this point.

What happens to the interference pattern when two coherent sources are

(a) infinitely close, and

(b) far apart from each other