Question

What is the effective focal length of the convex lenses of focal length 10 cm and 25 CM respectively are joined together?

Answer 1

The effective focal length is 7.14 cm.

Explanation:

Focal length of first convex lens, f1 = +10 cm

Focal length of second convex lens, f2= +25 cm

Let the focal length of combination is F, so

$\frac{1}{F} =\frac{1}{f_{1} } +\frac{1}{f_{2} }$

Substitute the given values, we get

$\frac{1}{F} =\frac{1}{10cm} } +\frac{1}{25cm} }$

$\frac{1}{F} =\frac{14}{100}$

$F=\frac{100}{14} =7.14$

Thus, the effective focal length is 7.14 cm.

Learn more: Combination of focal length.

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