Question

An optical system uses two thin convex lenses in contact having the effective focal length of 30/4cm If one lens has focal length of 30cm. find the focal length of the other lens please answer me ​

Answer 1

$\frac{1}{f} = \frac{1}{f1} + \frac{1}{f2}$

$\frac{30}{4} = \frac{1}{30} + \frac{1}{f2}$

$\frac{1}{f2} = \frac{30}{4} - \frac{1}{30}$

$\frac{1}{f2} = \frac{448}{60}$

$f2 = \frac{60}{448}$

f2=0.13 cm