Question

Two thin convex lens has focal length 15 cm and 10 cm then its effective focal length is

Answer 1

Answer:

Effective focal length f = 6 cm.

Explanation:

The power of a spherical lens is related to its focal length as

$P= \dfrac{1}{f}. \end{aligned}$

The total power of a series of thin lenses kept close together is given by $P_1 + P_2 +....$

Here, $f_1 = 0.15m$ and $f_2 = 0.1 m$.

$P = P_1 + P_2 =\dfrac{1}{0.1}+\dfrac{1}{0.15}$

$\begin{aligned}.\\=\dfrac{0\cdot 15+0.1}{0.015}\\=\dfrac{0.25}{0.015}=\dfrac{50}{3}\end{aligned}$

Now, the effective focal length, given by $f=\dfrac{1}{P}\\\\=\dfrac{3}{50}=0\cdot 06m\\\\=6 cm\end{aligned}$