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S E C T I O N 3 8 . 4 • The Diffraction Grating 1221 (a) the screen is moved to a distance 2L from the grating (b) the screen is moved to Conceptual Example 38.6 A Compact Disc Is a Diffraction Grating Light reflected from the surface of a compact disc is multicol- Solution The surface of a compact disc has a spiral grooved Figure 38.20 (Conceptual Example 38.6) A compact disc observed under white light. The colors observed in the reflected light and their intensities depend on the orientation of the disc relative to the eye and relative to the light source. © Kristen Brochmann/Fundamental Photographs Example 38.7 The Orders of a Diffraction Grating Monochromatic light from a helium–neon laser (% " Solution First, we must calculate the slit separation, which For the first-order maximum (m " 1), we obtain 22.311 !
1 " sin !
1 " % " 632.8 nm " 0.379 6 d " 1 6 000 cm " 1.667 & 10 ' 4 cm " 1 667 nm For the second-order maximum (m " 2), we find What If? What if we look for the third-order maximum? Do we find it? Answer For m " 3, we find sin ! 3 " 1.139. Because sin! cannot exceed unity, this does not represent a realistic solu- 49.391 !
2 " sin !
2 " 2% d " 2(632.8 nm) 1 667 nm " 0.759 2 Investigate the interference pattern from a diffraction grating at the Interactive Worked Example link at http://www.pse6.com. Resolving Power of the Diffraction Grating The diffraction grating is useful for measuring wavelengths accurately. Like the prism, Interactive |