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GRATINGS: Why Add More Slits?

GRATINGS: Why Add More Slits?. Principal maxima become sharper Increases the contrast between the principal maxima and the subsidiary maxima. Dispersion of a diffraction grating. Resolving power of a diffraction grating.

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GRATINGS: Why Add More Slits?

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  1. GRATINGS: Why Add More Slits? • Principal maxima become sharper • Increases the contrast between the • principal maxima and the subsidiary • maxima

  2. Dispersion of a diffraction grating

  3. Resolving power of a diffraction grating Rayleigh: principal maximum of one coincides with first minimum of the other

  4. Interference minima when

  5. From the condition for interference maxima:

  6. 2001 Q2 a) Show that an ideal diffraction grating with narrow slits spaced a distance d apart illuminated with light of wavelength l will produce an intensity pattern with peaks at angles q given by d sin (q) = n l, where n is an integer. b) If such a diffraction grating with 500 slits per mm is illuminated with 600 nm light, what is the maximum order of diffraction, n, that will be visible?

  7. 2001 Q13 a) Describe the difference between the conditions under which Fraunhofer and Fresnel diffraction may be observed. Show that the intensity distribution in the Fraunhofer pattern of a slit of width w illuminated with light of wavelength l is b) Describe Rayleigh's criterion for the resolution of images formed by a slit, and deduce from the above formula for the diffraction pattern that the minimum angular separation between two images which can just be resolved, at wavelength l, by a slit of width w, is l/w. c) State how this expression is modified for a circular aperture of diameter D. d) Use this result to calculate the smallest separation between two objects that can be resolved by a human eye with a pupil diameter of 2.5 mm at a distance of 250 mm, assuming a wavelength of 500 nm.

  8. GEOMETRIC OPTICS S&B: Chapter 36 Mirrors Lenses Compound systems Uses for above

  9. Mirrors Mirrors are used widely in optical instruments for gathering light and forming images since they work over a wider wavelength range and do not have the problems of dispersion which are associated with lenses and other refracting elements. Plane/flat Concave Convex We assume light goes from left to right

  10. Plane/Flat Mirrors object at distance p image at distance q erect/ upright

  11. Virtual image

  12. Images are located at the point from which rays of light actually diverge or at the point from which they appear to diverge. A real image is formed when light rays pass through and diverge from the image point. A virtual image is formed when the light rays do not pass through the image point but appear to diverge from that point.

  13. Front-back reversal

  14. For plane mirrors: The image is as far behind the mirror as the object is in front of the mirror. |p| = |q| The image is unmagnified, virtual, and upright. M = 1 (magnification) The image has front-back reversal.

  15. Magnification (lateral)

  16. Paraxial rays principal axis f = R/2 centre of curvature R

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