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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
A real object approa ches a fixed diverging lens with a constant velocity from infinity along the principal axis. The relative velocity between object and its image will be
  • A
    increasing
  • ✓
    decreasing
  • C
    first increasing then decreasing
  • D
    first decreasing and then increasing
✓

Answer

Correct option: B.
decreasing
b
$V_{1}=\frac{v^{2}}{u^{2}} V_{0} $ and $ v=\frac{u f}{-u-f} \Rightarrow \frac{-f}{u+f}=\frac{v}{u}$

$V_{\text {rel }}=V_{0}-V_{i}=\left(1-\frac{v^{2}}{u^{2}}\right) V_{0}$

$=\left[1-\left(\frac{f}{f+u}\right)^{2}\right] V_{0}$

as u increases $v_{ rel }$ decreases

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