Physics Class 12 NCERT Solutions: Chapter 9 Ray Optics and Optical Instruments Part 5 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Magnification Equation

Q: 11. A compound microscope consists of an objective lens of focal length and an eyepiece of focal length separated by a distance of . How far from the objective should an object be placed in order to obtain the final image at (a) the least distance of distinct vision , and (b) at infinity? What is the magnifying power of the microscope in each case?

Answer:

Focal length of the objective lens,

Focal length of the eyepiece,

Distance between the objective lens and the eyepiece,

(A) Least distance of distinct vision,

∴ Image distance for the eyepiece,

Object distance for the eyepiece

According to the lens formula, we have the relation:

Image distance for the objective lens,

Object distance for the objective lens

According to the lens formula, we have the relation:

Magnitude of the object distance,

The magnifying power of a compound microscope is given by the relation:

Hence, the magnifying power of the microscope is .

(B) The final image is formed at infinity.

∴ Image distance for the eyepiece,

Object distance for the eyepiece

According to the lens formula, we have the relation:

Image distance for the objective lens,

Object distance for the objective lens

According to the lens formula, we have the relation:

Magnitude of the object distance,

The magnifying power of a compound microscope is given by the relation:

Hence, the magnifying power of the microscope is .

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