A) 80 cm
B) 40 cm
C) 63 cm
D) 57 cm
Correct Answer: C
Solution :
To see with relaxed eye, final image should be formed at infinity. Length of telescope \[L={{f}_{0}}+{{f}_{e}}\] ... (i) and magnification\[M=\frac{{{f}_{0}}}{{{f}_{e}}}\] ... (ii) Given, M = 20, \[{{f}_{0}}=60\] \[\therefore \] \[{{f}_{e}}=\frac{60}{20}=3\,cm\] \[\therefore \] \[L={{f}_{0}}={{f}_{e}}\] = 60 + 3 = 63 cmYou need to login to perform this action.
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