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Optical Instruments — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysicsOptical Instruments3 Marks
Question
A simple microscope has a magnifying power of $3.0$ when the image is formed at the near point $(25\ cm)$ of a normal eye.
  1. What is its focal length?
  2. What will be its magnifying power if the image is formed at infinity?
✓

Answer

The simple microscope has, $m = 3,$ when image is formed at $D = 25\ cm$
  1. $\text{m}=1+\frac{\text{D}}{\text{f}}\Rightarrow3=1+\frac{25}{\text{f}}$
$\Rightarrow\text{f}=\frac{25}{2}=12.5\text{cm}$
  1. When the image is formed at infinity $($normal adjustment$)$
Magnifying power $=\frac{\text{D}}{\text{f}}=\frac{25}{12.5}= 2.0$

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