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Ray Optics — JEE physics STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 ScienceJEE physicsRay Optics1 Mark
MCQ
When a telescope is adjusted for parallel light, the distance of the objective from the eye piece is found to be $80 \mathrm{~cm}$. The magnifying power of the telescope is $19.$ The focal lengths of the lenses are
  • A
    $61 \mathrm{~cm}, 19 \mathrm{~cm}$
  • B
    $40 \mathrm{~cm}, 40 \mathrm{~cm}$
  • ✓
    $76 \mathrm{~cm}, 4 \mathrm{~cm}$
  • D
    $50 \mathrm{~cm}, 30 \mathrm{~cm}$
✓

Answer

Correct option: C.
$76 \mathrm{~cm}, 4 \mathrm{~cm}$
$f_o+f_e=80$ and $\frac{f_o}{f_e}=19 \Rightarrow f=76$ and $f=4 \mathrm{~cm}$.

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