Question

QUESTION 5. (5a) Distinguish between Fraunhofer and Fresnel diffraction, in terms of a criterion based on feature/aperture size, illumination wavelength, and distances to the source and field points (5b) Determine the smallest resolvable angular separation between two stars of equal bright- ness viewed at 550 nm through the 200-inch diameter Hale telescope on Mount Palomar, near San Diego, California. If the primary viewing focal length is 666 inches, what is the linear separation between the images? (1 inch 25.4 mm) 8 marks] [12 marks]

Answer 1

Fraunhofer and Fresnel Diffraction . Diffraction phenomena can be classified either as Fraunhofer diffraction or Fresnel diffraction. The observable difference: Fresnel diffraction The viewing screen and the aperture are located close together, the image of the aperture is clearly recognisable despite slight fringing around its periphery -As the separation between the screen and the aperture increases, the image of the aperture becomes increasingly more structured; fringes become more prominent. Fraunhofer diffraction The viewing screen and the aperture separated by a large distance, the projected patterm bears little or no resemblance to the aperture As the separation increases, the size of the patten changes but not its shape

1220_ -9 1.22乂SSoxio Sec 202.2 m microndre

Please Rate Thank So much