A) \[164\,\,cm\]
B) \[124\,\,cm\]
C) \[100\,\,cm\]
D) \[84\,\,cm\]
Correct Answer: A
Solution :
Magnification for parallel rays, \[m=\frac{{{f}_{o}}}{{{f}_{e}}}\] \[\Rightarrow \] \[20=\frac{80}{{{f}_{e}}}\] or \[{{f}_{e}}=4\,\,cm\] If the focal length of erecting lens is\[20\,\,cm\], then the length of the telescope \[{{L}_{\infty }}={{f}_{o}}+4f+{{f}_{e}}\][where,\[f\] is the focal length of erecting lens] \[=80+4\times 20+4\] \[=80+80+4=164\,\,cm\]You need to login to perform this action.
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