Question

two lenses of power +3.5 D and -2.5D are placed in contact find the power and the focal length of the combination

Answer 1

effective power=P1+P2

=3.5-2.5

=1D

power=1/focal length

P=1/f

f=1/P

f=1m

Answer 2

Hi there

for finding out the power of the combination

Ptot=P1+P2

=3.5+(-2.5)

=1D

also

P=1/F

=1/1

=1m