Question 292: Ray Optics

Question

In the figure shown here, what is the equivalent focal length of the combination of lenses (Assume that all layers are thin) ?

Accepted Answer

Use $$\frac{1}{\mathrm{f}}=[\mu-1]\left[\frac{1}{\mathrm{R}_{1}}-\frac{1}{\mathrm{R}_{2}}\right]$$
$$\frac{1}{\mathrm{f}_{1}}=[1.6-1]\left[\frac{1}{\infty}-\frac{1}{20}\right]=\frac{-3}{100}$$
$$\frac{1}{\mathrm{f}_{2}}=[1.5-1]\left[\frac{1}{20}+\frac{1}{20}\right]=\frac{1}{20}$$
$$\frac{1}{\mathrm{f}_{3}}=\frac{-3}{100}$$
$$\frac{1}{f_{e q}}=\frac{1}{f_{1}}+\frac{1}{f_{2}}+\frac{1}{f_{3}}$$
$$\frac{1}{f_{e q}}=-\frac{3}{100}+\frac{1}{20}-\frac{3}{100}=\frac{-1}{100}$$

Answer

$$-40 \mathrm{~cm}$$

Answer

$$-100 \mathrm{~cm}$$

Answer

$$-50 \mathrm{~cm}$$

Answer

$$40 \mathrm{~cm}$$

Ray Optics

In the figure shown here, what is the equivalent focal length of the combination of lenses (Assume that all layers are thin) ?

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