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Ray Optics and Optical Instruments — Physics STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 SciencePhysicsRay Optics and Optical Instruments5 Marks
Question
  1. Draw a ray diagram showing the image formation by a compound microscope. Hence obtain expression for total magnification when the image is formed at infinity.
  2. Distinguish between myopia and hypermetropia. Show diagrammatically how these defects can be corrected.
✓

Answer

  1. Difference between myopia and hypermetropia
Myopia

Hypermetropia
  1. The eye ball is elongated.
  1. The eye ball is shortened.
  1. Person cannot see distant objects clearly.
  1. Person cannot see near objects clearly.
  • Myopic eye is corrected by interposing a concave lens between eye and object.
  • Hypermetropia is corrected by interposing a convex lens between eye and object.

  1. If image A 'B' is exactly at the focus of the eyepiece, then image A "B" is formed at infinity. If the object AB is very close to the focus of the objective lens of focal length fo, then magnification Mo by the objective lens

$\text{M}_{e} = \frac{\text{L}}{\text{f}_{o}}$

where L is tube length (or distance between lenses Lo and Le)

Magnification Me by the eyepiece

$\text{M}_{e} = \frac{\text{D}}{\text{f}_{e}}$

where D = Least distance of distinct vision Total magnification m = MoMe

$ = \bigg(\frac{\text{L}}{\text{f}_{o}}\bigg)\bigg(\frac{\text{D}}{\text{f}_{e}}\bigg).$

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