Convex lens of 10 cm focal length is combined with a concave lens of 6 cm focal length. Find the focal length of the combination.
Answer & explanation
Correct answer: option 2
Here f1 = 10 cm, f2 = -6 cm, F = ?
Use the formula $\frac{1}{F}=\frac{1}{f_1}+\frac{1}{f_2}=\frac{1}{10}-\frac{1}{6}=-\frac{1}{15}$
∴ F = −15 cm