Question

Two thin lenses of focal length +30 cm and 15 cm are kept in contact. the power of the combination is

Answer 1

Answer:

$power = \frac{1}{feq}$

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

feq=0.15m hence power =6.6 dioptre

Answer 2

Answer:

focal length of the combination is f1+f2=30-15=15cm

power=100/F

=100/15

=6.67