Rankers Physics

Refraction by Spherical Surfaces: Practice Problem & Solution

A convex lens and a concave lens, each having same focal length of $25 cm$, are put in contact to form a combination of lenses. The power in diopters of the combination is: (2006)
$25$
$50$
Infinite
Zero

Solution Explained:

To solve this problem, we apply the core principles of Refraction by Spherical Surfaces. Understanding the underlying formula is key to arriving at the correct answer below:

For the convex lens, $f_1 = +25 cm$, and for the concave lens, $f_2 = -25 cm$. Equivalent power is $P = P_1 + P_2 = \frac{100}{f_1} + \frac{100}{f_2}$. $P = \frac{100}{25} - \frac{100}{25} = 0$.

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