Question

the focal length of a convex lens is 100/3 cm and that of concave lens is 50/3 cm.find the power and focal length of this combination.

Answer 1

$$\begin{gathered} Thepoweroftheconvexlens,P_1=\frac{1}{f}=\frac{3x100}{100}=3D \\ Thepoweroftheconcavelens,P_2=\frac{1}{f}=\frac{-3x100}{50}=-6D \end{gathered}$$

The combination of power of the lenses will be :- P = P₁₊ P_{2 =} -6D+ 3D = - 3D
As, focal length = 1 / power

$f=\frac{1}{-3}meters.$