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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
In optical bench experiment index error is $+1\ cm$ and $-1\ cm$ , between object needle and lens, lens and image needle respectively. Observed values of $u$ and $v$ are $9\ cm$ and $17\ cm$ . Focal length of lens is .....$cm$
  • A
    $6.15$
  • ✓
    $5.54$
  • C
    $5.88$
  • D
    $6.25$
✓

Answer

Correct option: B.
$5.54$
b
Index error in $\mathrm{u}=+1 \mathrm{\,cm}$

$\mathrm{u}=8 \mathrm{\,cm}$

index error in $\mathrm{v}=-1 \mathrm{\,cm}$

$v=17+1=18 \mathrm{\,cm}$

$\frac{1}{f}=\frac{1}{18}+\frac{1}{8}$

$\mathrm{f}=5.53 \mathrm{\,cm}$

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