Q. Two lenses of power +12 and $- 2$ dioptres are placed in contact. What will the focal length of combination
A) $10\ cm$
B) $12.5\ cm$
C) $16.6\ cm$
D) $8.33\ cm$
Explanation
(a) Power of the combination $P = P_{1} + P_{2} = 12 - 2 = 10\ D$
$\therefore\ $Focal length of the combination
$F = \frac{100}{P} = \frac{100}{10} = 10\ cm$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.