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| Numerical - 33 |
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| 33. A diffraction grating one cm wide has 1000 lines and is used in the third over. What are the diffraction angles for violet and orange lights? What is the angular size of the diffraction maximum for monochromatic light? The wavelengths for violet and orange are 400 nm and 600 nm respectively. |
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| Suggested solution: |
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| The spectrum is thus spread over an angle of nearly 3.40. |
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| The path difference between the first and the last slit in the grating is an integral number of wavelengths. Let us increase q so that an extra path difference of l is introduced across the width w. The change in q required to do this is denoted by Dq. |
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| Because of the 3600 extra phase across the grating, we can divide it into two halves again so that there is a 1800 phase difference between slits separated by w/2. So, we get zero intensity at |
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| It may be noted here that the maximum is sufficiently sharp. |
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