Read the following statements related to telescopes carefully:
(A) The main considerations of an astronomical telescope are its light gathering power and its resolution.
(B) the ability to observe two objects (very nearly in the same direction) distinctly depends on the diameter of the objective
(C) large-sized lenses which form images that are free from any kind of chromatic aberration and distortions can be made easily
(D) Telescopes with mirror objectives are free from chromatic aberration
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A), (B) and (D) only
(A) The main considerations of an astronomical telescope are its light gathering power and its resolution. — Correct. A large objective collects more light and separates close objects better.
(B) The ability to observe two objects (very nearly in the same direction) distinctly depends on the diameter of the objective. — Correct. The resolving power grows with the diameter of the objective.
(C) Large-sized lenses which form images that are free from any kind of chromatic aberration and distortions can be made easily. — Incorrect. Large lenses are heavy, sag under their own weight and are very hard to make free of aberrations.
(D) Telescopes with mirror objectives are free from chromatic aberration. — Correct. Reflection does not depend on wavelength, so a mirror objective has no chromatic aberration.
NCERT (2026-27):
Telescope – “… The main considerations with an astronomical telescope are its light gathering power and its resolution or resolving power. … The resolving power, or the ability to observe two objects distinctly, which are in very nearly the same direction, also depends on the diameter of the objective. … Further, it is rather difficult and expensive to make such large sized lenses which form images that are free from any kind of chromatic aberration and distortions. … Telescopes with mirror objectives are called reflecting telescopes. There is no chromatic aberration in a mirror.”