Question

Find the half angular width of the central bright maximum in the Fraunhofer diffraction pattern of a = 12 x 10^-5 cm wide slit when the slit is illuminated by mono-chromatic light of wavelength 600 nm.

Answer 1

The width of the slit, a= 12 times 10^-5 cm = 12 times 10^-2m. The wavelength of light, lambda - 600 nm = 600 times 10^-9m we know that, a sin theta = m lambda For, m = 1 DoubleRightArrow theta = sin^-1[lambda/a] theta = sin^-1[600 times 10^-9/12 times 10^-7] = sin^-1[0.5] theta = 30 degree therefore the half angular width of central bright: maxima, theta = 30 degree.