b
કોણીય પહોળાઈ \( = \,\,\,2\,\theta \,\, = \,\,\,\frac{{2\lambda }}{d}\,\, = \,\,\frac{{2\,\, \times \,\,6000\,\,\, \times \,\,{{10}^{ - 10}}}}{{18\,\, \times \,\,{{10}^{ - 5}} \times \,\,\,{{10}^{ - 2}}}}\,\,\, = \,\,\frac{2}{3}\)
\( = \,\,\,\frac{2}{3}\,\,\,rad\,\,\, = \,\,\frac{2}{3}\,\, \times \,\,\,\frac{{180}}{\pi }\,\, = \,\,\,{40^ \circ }\)