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DIFFREITHIANT

DIFFREITHIANT. Mae diffreithiant golau yn cael ei esbonio gan y ffaith bod golau yn teithio fel cyfres o flaendonnau. Wrth i’r golau deithio drwy hollt mae’r blaendonnau yn diffreithio ar ymyl yr hollt. Mae hyn yn gallu achosi i’r blaendonnau ffurfio blaendonnau crwm.

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DIFFREITHIANT

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  1. DIFFREITHIANT • Mae diffreithiant golau yn cael ei esbonio gan y ffaith bod golau yn teithio fel cyfres o flaendonnau. • Wrth i’r golau deithio drwy hollt mae’r blaendonnau yn diffreithio ar ymyl yr hollt. Mae hyn yn gallu achosi i’r blaendonnau ffurfio blaendonnau crwm. Wrth ymyrru gyda’i gilydd mae dau set o flaendonnau sydd mewn cydwedd yn creu patrwm ymyriant. Gall ymyl miniog megis nodwydd neu lafn cyllell hefyd greu diffreithiant i donnau o olau.

  2. Diffreithiant gan hollt sengl Minimwm 1af

  3. ARBRAWF THOMAS YOUNG

  4. Ymyriant distrywiol P1 r1  r2 a/2  P0 a/2 Gwahaniaeth llwybr Golau trawol Mae’r golau sy’n teithio drwy pob rhan o’r hollt ( o led a) mewn cydwedd a’i gilydd. Bydd y golau ar P0 yn ymyru yn adeiladol gan greu yr eddï llachar yn y canol.

  5. destructive interference P1 r1  r2 a/2  P0 a/2 path difference (x) incident light To find the first minimum we divide the slit into two equal parts a/2. The ray coming from the top of the upper portion (r1) will interfere with the light coming from the top of the lower portion (r2). The path difference will be x = (a/2) sin  = /2 (for destructive interference) (1)

  6. destructive interference P1 r1  r2 a/2  P0 a/2 path difference (x) incident light D For each ray r1 proceeding from the top portion there will be a ray r2 proceeding from the bottom portion with the same path difference as for the two rays shown. If D >> a, then the rays can be considered essentially parallel, and the two angles shown as  are approximately equal.

  7. The position of the first minimum is given by a sin  =  The position of the second minimum can be found by dividing the slit into 4 portions and proceeding as before. The general result is a sin  = m, m is an integer for the positions of the minima. The maxima are found by assuming that they lie half way between the minima.

  8. Intensity in Single-slit Diffraction The intensity in a single-slit diffraction pattern is given by where Im = the maximum intensity and

  9. I (relative intensity) 1 a =  20 0 20  (degrees)

  10. I (relative intensity) 1 a = 5 20 0 20  (degrees)

  11. I (relative intensity) 1 a = 10 20 0 20  (degrees)

  12. Diffraction by a Double Slit • In previous discussion of double slit interference we ignored the single slit diffraction effects produced by the individual slits. • This is reasonable if the width of the slits is much less than the wavelength of the illuminating light (see diagrams of intensity for single slit diffraction) as the central maximum will be large and of approximately constant brightness.

  13. The intensity of the combined pattern (single-slit diffraction together with double-slit interference) is given by where d is the distance between the slits, while a is the width of the slits, and  is the angle from the straight through position.

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