Define in one sentence each the Least distance of distinct vision

What is the least distance of distinct vision ?

A compound microscope consists of an objective lens of focal length 2.0 cm and an eyepiece of focal length 6.25 cm separated by a distance of 15cm. 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 (25cm), and (b) at infinity? What is the magnifying power of the microscope in each case?

A small telescope has an objective lens of focal length 140cm and an eyepiece of focal length 5.0cm. 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 (25cm)?

The focal length of objective and eye lens of a astronomical telescope are respectively 2m and 5 cm . Final image is formed at (i) least distance of distinct vision (ii) infinity. The magnifying power in both cases will be

Define digestion in one sentence.

A compound microscope has an objective of focal length 2.0 cm and an eye-piece of focal length 6.25cm and distance between the objective and eye-piece is 15cm . If the final image is formed at the least distance vision (25 cm) , the distance of the object form the objective is

For hearing distinct echo, the minimum distance of the obstacle from the source of sound should be ....... m. (10.2, 34.4, 17.2)