logging in or signing up DIFFRACTION louise.woolford Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINT lite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 307 Category: Entertainment License: All Rights Reserved Like it (1) Dislike it (0) Added: July 14, 2009 This Presentation is Public Favorites: 1 Presentation Description No description available. Comments Posting comment... By: guitar79 (9 month(s) ago) What a nice presentation Saving..... Post Reply Close Saving..... Edit Comment Close By: haniaasad (17 month(s) ago) i see it as a good conceptual presentation, provided enough data for the common understanding Saving..... Post Reply Close Saving..... Edit Comment Close Premium member Presentation Transcript Slide 1: John Parkinson © 1 DIFFRACTION DIFFRACTION Slide 2: John Parkinson © 2 THE BENDING OF WAVES AROUND CORNERS - PAST AN OBSTACLE OR THROUGH A GAP Single Slit Diffraction Slide 3: John Parkinson © 3 HUYGEN’s CONSTRUCTION FOR A PLANE WAVEFRONT “Every point on a wavefront acts as a source of secondary waves which travel with the speed of the wave. At some subsequent time the envelope of the secondary waves represents the new position of the wavefront.” Slide 4: John Parkinson © 4 wide gap narrow gap The central maximum is twice the width of the other maxima The central maximum is lower [less energy passes through], but wider Slide 5: John Parkinson © 5 ? For first minimum sin ? = l/d Or for small angles in radians ? = l/d d = width of the gap Slide 6: John Parkinson © 6 http://webphysics.ph.msstate.edu/javamirror/ipmj/java/slitdiffr/index.html At this web site you can change the width of the slit and the wavelength to see how theses factors affect the diffraction pattern Slide 7: John Parkinson © 7 The double slit pattern is superimposed on the much broader single slit diffraction pattern. The bright central maximum is crossed by the double slit interference pattern, but the intensity still falls to zero where minima are predicted from single slit diffraction. The brightness of each bright fringe due to the double slit pattern will be “modulated” by the intensity envelope of the single slit pattern. Diffraction by a Double Slit The double slit fringes are still in the same place Slide 8: John Parkinson © 8 DIFFRACTION GRATING Each slit effectively acts as a point source, emitting secondary wavelets, which add according to the principle of superposition n=1 corresponds to a path difference of one wavelength n=2 corresponds to a path difference of two wavelengths n=3 corresponds to a path difference of three wavelengths Slide 9: John Parkinson © 9 Monochromatic light ? C ? For light diffracted from adjacent slits to add constructively, the path difference = AC must be a whole number of wavelengths. AC = AB sin ? and AB is the grating element = d Hence d sin ? = n? d = grating element A B Slide 10: John Parkinson © 10 DIFFRACTION GRATINGS WITH WHITE LIGHT PRODUCE SPECTRA Slide 11: John Parkinson © 11 DIFFRACTION GRATING WITH WHITE LIGHT Hence in any order red light will be more diffracted than blue. White Central maximum, n = 0 First Order maximum, n = 1 First Order maximum, n = 1 Second Order maximum, n = 2 Second Order maximum, n = 2 Several spectra will be seen, the number depending upon the value of d A spectrum will result screen Slide 12: John Parkinson © 12 n=0 n=2 n=1 n=3 grating Note that higher orders, as with 2 and 3 here, can overlap Be aware that in the spectrum produced by a prism, it is the blue light which is most deviated Slide 13: John Parkinson © 13 QUESTION 1 Given a grating with 400 lines/mm, how many orders of the entire visible spectrum (400 – 700 nm) can be produced? Finding the spacing d of the “slits” (lines). d = 1/400 = 2.5 x 10-3 mm = 2.5 x 10-6 m d sin ? = n? sin ? = (n ?)/d = a maximum of 1 at 900 Why do we use 700 nm? Hence there are 7 orders in all (white central order + 3 on each side) Slide 14: John Parkinson © 14 Question 2: Visible light includes wavelengths from approximately 400 nm (blue) to 700 nm (red). Find the angular width of the second order spectrum produced by a grating ruled with 400 lines/mm. As before d = 2.5 x 10-6 m For red light in the second order For blue light in the second order 34.1 - 18.7 = 15.40 You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.
DIFFRACTION louise.woolford Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINT lite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 307 Category: Entertainment License: All Rights Reserved Like it (1) Dislike it (0) Added: July 14, 2009 This Presentation is Public Favorites: 1 Presentation Description No description available. Comments Posting comment... By: guitar79 (9 month(s) ago) What a nice presentation Saving..... Post Reply Close Saving..... Edit Comment Close By: haniaasad (17 month(s) ago) i see it as a good conceptual presentation, provided enough data for the common understanding Saving..... Post Reply Close Saving..... Edit Comment Close Premium member Presentation Transcript Slide 1: John Parkinson © 1 DIFFRACTION DIFFRACTION Slide 2: John Parkinson © 2 THE BENDING OF WAVES AROUND CORNERS - PAST AN OBSTACLE OR THROUGH A GAP Single Slit Diffraction Slide 3: John Parkinson © 3 HUYGEN’s CONSTRUCTION FOR A PLANE WAVEFRONT “Every point on a wavefront acts as a source of secondary waves which travel with the speed of the wave. At some subsequent time the envelope of the secondary waves represents the new position of the wavefront.” Slide 4: John Parkinson © 4 wide gap narrow gap The central maximum is twice the width of the other maxima The central maximum is lower [less energy passes through], but wider Slide 5: John Parkinson © 5 ? For first minimum sin ? = l/d Or for small angles in radians ? = l/d d = width of the gap Slide 6: John Parkinson © 6 http://webphysics.ph.msstate.edu/javamirror/ipmj/java/slitdiffr/index.html At this web site you can change the width of the slit and the wavelength to see how theses factors affect the diffraction pattern Slide 7: John Parkinson © 7 The double slit pattern is superimposed on the much broader single slit diffraction pattern. The bright central maximum is crossed by the double slit interference pattern, but the intensity still falls to zero where minima are predicted from single slit diffraction. The brightness of each bright fringe due to the double slit pattern will be “modulated” by the intensity envelope of the single slit pattern. Diffraction by a Double Slit The double slit fringes are still in the same place Slide 8: John Parkinson © 8 DIFFRACTION GRATING Each slit effectively acts as a point source, emitting secondary wavelets, which add according to the principle of superposition n=1 corresponds to a path difference of one wavelength n=2 corresponds to a path difference of two wavelengths n=3 corresponds to a path difference of three wavelengths Slide 9: John Parkinson © 9 Monochromatic light ? C ? For light diffracted from adjacent slits to add constructively, the path difference = AC must be a whole number of wavelengths. AC = AB sin ? and AB is the grating element = d Hence d sin ? = n? d = grating element A B Slide 10: John Parkinson © 10 DIFFRACTION GRATINGS WITH WHITE LIGHT PRODUCE SPECTRA Slide 11: John Parkinson © 11 DIFFRACTION GRATING WITH WHITE LIGHT Hence in any order red light will be more diffracted than blue. White Central maximum, n = 0 First Order maximum, n = 1 First Order maximum, n = 1 Second Order maximum, n = 2 Second Order maximum, n = 2 Several spectra will be seen, the number depending upon the value of d A spectrum will result screen Slide 12: John Parkinson © 12 n=0 n=2 n=1 n=3 grating Note that higher orders, as with 2 and 3 here, can overlap Be aware that in the spectrum produced by a prism, it is the blue light which is most deviated Slide 13: John Parkinson © 13 QUESTION 1 Given a grating with 400 lines/mm, how many orders of the entire visible spectrum (400 – 700 nm) can be produced? Finding the spacing d of the “slits” (lines). d = 1/400 = 2.5 x 10-3 mm = 2.5 x 10-6 m d sin ? = n? sin ? = (n ?)/d = a maximum of 1 at 900 Why do we use 700 nm? Hence there are 7 orders in all (white central order + 3 on each side) Slide 14: John Parkinson © 14 Question 2: Visible light includes wavelengths from approximately 400 nm (blue) to 700 nm (red). Find the angular width of the second order spectrum produced by a grating ruled with 400 lines/mm. As before d = 2.5 x 10-6 m For red light in the second order For blue light in the second order 34.1 - 18.7 = 15.40