Question

In a compound microscope, maximum magnification is obtained when the final image

• A. Is formed at the least distance of distinct vision
• B. Is formed at infinity
• C. Coincides with the object
• D. Coincides with the objective lens

Answer 1

The correct option is A

Is formed at the least distance of distinct vision

Correct Option: Option A

1. Compound Microscope: An optical microscope with a high resolution that consists of two sets of lenses and provides a two-dimensional image of the object is known as a compound microscope. It uses two types of lenses, namely, the objective lens, which is placed close to the object, and the eyepiece, through which one looks at the image.
2. Magnification: The magnification of a compound microscope is the product of the magnification of the objective lens and magnification of the eyepiece $M=m_o{m}_e=\left(\frac{L}{f_o}\right)\left(1+\frac{D}{f_e}\right)$, where $m_o$ is the magnification of the objective lens, $m_e$ is the magnification of eye piece, $f_o$ and $f_e$ are focal lengths of the objective lens and eyepiece respectively and $D$ is the least distance of distinct vision.
3. The magnification is maximum when the image is formed at least at a distance of distinct vision. So, this option is correct.

Incorrect Options:

Option B

When an image is formed at infinity, the formula for magnification of the compound microscope is $M=\left(\frac{L}{f_o}\right)\left(\frac{D}{f_e}\right)$, which is not the maximum. So, this option is incorrect.

Option C

When the image coincides with the object, its magnification won't be maximum. So, this option is incorrect.

Option D

When the image coincides with the objective lens, its magnification won't be maximum. So, this option is incorrect.

Hence, the correct option is option A.