A) 100cm
B) 10cm
C) 20cm
D) 25cm
Correct Answer: A
Solution :
To see with relaxed eye, final image should be formed at infinity. The length of telescope is given by \[L={{f}_{0}}+{{f}_{e}}\] ... (i) and magnifying power \[M=\frac{{{f}_{o}}}{{{f}_{e}}}\] ... (ii) Given, L = 105, M = 20 \[\therefore \] \[{{f}_{0}}+{{f}_{e}}=105\] ... (iii) \[\frac{{{f}_{o}}}{{{f}_{e}}}=20\] ... (iv) From Eqs. (iii) and (iv), we get \[20\,\,{{f}_{e}}+{{f}_{e}}=105\] \[\Rightarrow \] \[21{{f}_{e}}=105\] \[\Rightarrow \] \[{{f}_{e}}=\frac{105}{21}=5\,cm\] \[\Rightarrow \] \[{{f}_{o}}=105-5=100\,\,cm\]You need to login to perform this action.
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