Diffraction, gratings, resolving power

Diffraction, gratings, resolving power - Physics 102...

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Unformatted text preview: Physics 102: Lecture 20, Slide 1 Diffraction , Gratings, Resolving Power Physics 113 Dr. Renat Letfullin Physics 102: Lecture 20, Slide 2 Single Slit Diffraction Physics 113 Dr. Renat Letfullin Physics 102: Lecture 20, Slide 3 Wall Screen with opening (or obstacle without screen) shadow bright This is not what is actually seen! Diffraction Rays Physics 102: Lecture 20, Slide 4 • • Diffraction/ Huygens Every point on a wave front acts as a source of tiny wavelets that move forward. We will see maxima and minima on the wall. Light waves originating at different points within opening travel different distances to wall, and can interfere! Physics 102: Lecture 20, Slide 5 1 st minima Central maximum Physics 113 Dr. Renat Letfullin Physics 102: Lecture 20, Slide 6 W w 2 sin θ θ θ θ W 2 1 1 ′ Rays 2 and 2 ′ also start W/2 apart and have the same path length difference. 2 2 ′ 1 st minimum at sin θ = λ /w When rays 1 and 1 ′ interfere destructively. w 2 sin θ = λ 2 Under this condition, every ray originating in top half of slit interferes destructively with the corresponding ray originating in bottom half. Single Slit Diffraction Physics 102: Lecture 20, Slide 7 w Rays 2 and 2 ′ also start w/4 apart and have the same path length difference. 2 nd minimum at sin θ = 2 λ /w Under this condition, every ray originating in top quarter of slit interferes destructively with the corresponding ray originating in second quarter. Single Slit Diffraction 4 w θ 1 1 ′ ) sin( 4 w θ 2 2 ′ When rays 1 and 1 ′ will interfere destructively . 2 ) sin( 4 w λ θ = Physics 102: Lecture 20, Slide 8 Condition for quarters of slit to destructively interfere sin θ = m λ w (m=1, 2, 3, …) Single Slit Diffraction Summary Condition for halves of slit to destructively interfere w λ θ = ) sin( w λ θ 2 ) sin( = Condition for...
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This note was uploaded on 03/08/2009 for the course PH 113 taught by Professor Joenathan during the Fall '08 term at Rose-Hulman.

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Diffraction, gratings, resolving power - Physics 102...

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