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9. Ray optics abd optical instruments — Physics STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 SciencePhysics9. Ray optics abd optical instruments1 Mark
MCQ
The distance between a convex lens and a plane mirror is $10 \,cm$. The parallel rays incident on the convex lens after reflection from the mirror form image at the optical centre of the lens. Focal length of lens will be.....$cm$
  • A
    $10$
  • ✓
    $20$
  • C
    $30$
  • D
    Cannot be determined
✓

Answer

Correct option: B.
$20$
b
(b) From the figure,
Using property of plane mirror
Image distance $=$ Object distance
$f -10 = 10  \Rightarrow f = 20{\rm{ }}cm$

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