Lecture_19

Lecture_19 - Lecture 19-1 Lecture Diffraction by a Single...

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Lecture 19 Lecture 19 -1 Diffraction by a Single Slit (again) •When D >> a , the pair of rays are roughly parallel and their path difference is then (a/2) sin θ . • Divide the slit into two equal zones. A point source of wavelet in the upper zone always has a corresponding source in the lower zone that is at a distance a/2 away. sin 22 sin a a λ = = destructive interference dark fringes!
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Lecture 19 Lecture 19 -2 Single-slit Intensity Distribution: Example ( ) sin 0 am m θλ = Minima at ¾ For a given order minimum m , smaller a implies larger θ . That is, the smaller the slit width a , the broader the fringes . ¾ m = 0 => = 0 is a maximum.
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Lecture 19 Lecture 19 -3 Physics 219 – Question 1 – March 28, 2011. Which of the following changes on a single-slit diffraction experiment using red light from a laser results in increasing the separation between bright fringes? Assume that all else remains unchanged. A. Change the laser to one of green light B. Increasing the width of the slit C. Immerse the apparatus in water (assume the experiment could still be conducted) D. Increasing the power of the laser source E. Decreasing the width of the slit
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Lecture 19 Lecture 19 -4 Diffraction from Multiple Slits of Finite Width Two slits of width a λ or greater a From center to first min.= 1 1 sin / 2 d ⎛⎞ ⎜⎟ ⎝⎠
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Lecture 19 Lecture 19 -5 Diffraction Gratings • Devices that have a great number of narrow slits or rulings to produce an interference pattern with narrow fringes.
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Lecture_19 - Lecture 19-1 Lecture Diffraction by a Single...

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