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| Numerical - 23 |
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| 23. What is the minimum aperture of the objective of a telescope, which will enable two neighboring stars to be seen separately? The angle subtended by the two stars at the objective of telescope is 3 x 10-6 radian. l= 546 nm. |
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| The two stars will just appear separate if the principal maximum due to one coincides with the first minimum of the other in diffraction pattern. In other words, the half angular width of diffraction maximum is equal to the angle subtended by the stars at the objective of telescope of d is the aperture of telescope objective. |
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