A) 164 cm
B) 124 cm
C) 100 cm
D) 84 cm
Correct Answer: A
Solution :
Magnification for parallel rays, \[m=\frac{{{f}_{0}}}{{{f}_{e}}}\] \[\Rightarrow \] \[20=\frac{80}{{{f}_{e}}}\] or \[{{f}_{e}}=4cm\] If the focal length of erecting lens is 20 cm, then the length of the telescope \[{{L}_{\infty }}={{f}_{0}}+4f+{{f}_{e}}\] [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.
You will be redirected in
3 sec
