Question

Two lenses of power +3.5 D and -1.5 D are placed in contact. What is the power and focal length of the combination?​

Answer 1

Answer:

Power=2.0D

focal length

$p = 1 \div f \\ 2 = 1 \div f \\ f = 1 \div 2 \\ f = 0.5m$

Answer 2

Answer:

power= 2Dand f=1/2

Explanation:

power=3.5+(-1.5)

           =2D

Focal length=1/power

                    = 1/2