Question

An astronomical telescope with magnification 50 is to be designed in normal adjustment. Length of the tube is 102 cm. The powers of objective and eyepiece are respectively

• A. 2D, 50 D
• B. 1.5D, 20 D
• C. 1D, 40 D
• D. 1D, 50 D

Answer 1

The correct option is D 1D, 50 D

$M=50$

$u_e=f_e$

$M_{\infty }=\frac{f_o}{f_e}$

$L_{\infty }=f_o+f_e=102$

$\frac{f_o}{f_e}=50$

$f_o=50f_e$

$P_e=\frac{100}{2}=50D$

$P_o=1D$

$L_{\infty }=51f_e=102$

$f_e=2cm$

$f_o=100cm$