The focal length of the objective of a terrestrial telescope is 80 cm and it is adjusted for parallel rays, then its magnifying power is 20. If the focal length of erecting lens is 20 cm , then full length of telescope will beA. 84 cmB. 100 cmC. 124 cmD. 164 cm

The focal length of the objective of a terrestrial telescope is 80 cm

1.	The focal length of the objective of a terrestrial telescope is 80 cm and it is adjusted for parallel rays, then its magnifying power is 20. If the focal length of erecting lens is 20 cm , then full length of telescope will beA. 84 cmB. 100 cmC. 124 cmD. 164 cm
Answer» Correct Answer - D (d) For terrestrial telescope magnification, `M=f_(o)/(f_(e))=80/(f_(e))=20` `rArr f_(e)=4 cm` Hence, length of terrestrial telescope =`f_(o)+f_(e)+4f` `=80+4+4xx20` =164 cm

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The focal length of the objective of a terrestrial telescope is 80 cm and it is adjusted for parallel rays, then its magnifying power is 20. If the focal length of erecting lens is 20 cm , then full length of telescope will beA. 84 cmB. 100 cmC. 124 cmD. 164 cm

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