The parameter to be increased in order to increase the angular magnification of a simple microscope is
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → power of the lens
The angular magnification of a simple microscope (image at the near point \( D = 25\,\mathrm{cm} \)) is
\( \displaystyle m = 1 + \frac{D}{f} = 1 + D\,P \)
where \( P = 1/f \) is the power of the lens. A larger power (shorter focal length) gives a larger magnification.
Option (1) aperture of the lens — Incorrect. The aperture affects the brightness and the resolution, not the angular magnification.
Option (2) size of the object — Incorrect. Angular magnification is a ratio of angles; it does not depend on the size of the object.
Option (3) power of the lens — Correct. \( m = 1 + DP \) increases with the power.
Option (4) focal length of the lens — Incorrect. A larger focal length makes \( D/f \) smaller and lowers the magnification.
NCERT (2026-27):
The Microscope – “… Now according to our sign convention, v is negative, and is equal in magnitude to D. Thus, the magnification is
\( \displaystyle m = 1 + \frac{D}{f} \qquad (9.39) \)
Since D is about 25 cm, to have a magnification of six, one needs a convex lens of focal length, f = 5 cm.”