Physics Class 12 NCERT Solutions: Chapter 9 Ray Optics and Optical Instruments Part 15

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Ray diagram of telescope

Ray Diagram of Telescope

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Q: 33. An angular magnification (magnifying power) of is desired using an objective of focal length and an eyepiece of focal length. How will you set up the compound microscope?

Answer:

Focal length of the objective lens,

Focal length of the eyepiece,

Least distance of distinct vision,

Angular magnification of the compound microscope

Total magnifying power of the compound microscope,

The angular magnification of the eyepiece is given by the relation:

The angular magnification of the objective lens is related to me as:

We also have the relation:

Applying the lens formula for the objective lens:

The object should be placed away from the objective lens to obtain the desired magnification.

Applying the lens formula for the eyepiece:

Where,

Image distance for the eyepiece

Object distance for the eyepiece

Separation between the objective lens and the eyepiece

Therefore, the separation between the objective lens and the eyepiece should be.

Q: 34. A small telescope has an objective lens of focal length and an eyepiece of focal length. What is the magnifying power of the telescope for viewing distant objects when

(A) The telescope is in normal adjustment (i.e., when the final image is at infinity)?

(B) The final image is formed at the least distance of distinct vision?

Answer:

Focal length of the objective lens,

Focal length of the eyepiece,

Least distance of distinct vision,

(A) When the telescope is in normal adjustment, its magnifying power is given as:

(B) When the final image is formed at, the magnifying power of the telescope is given as: