Question

A convex lens of focal length 40cm is in contact with a concave lens of focal length 25cm . Calculate the power combination ?

Answer 1

Power of lens

$= 100 \div f \: in \: cm \\ p \: of convex \: lens \: = 100 \div 40 = 2.5 d \\ p \: of \: concave \: lens \: will \: be = 100 \div - 25 = - 4d$

so power combination of this bi focal lens will be -1.5D