Question

What will be the power of combination if a convex lens of focal length 20 cm and a concave lens of focal length 5 cm are combined together

Answer 1

Answer:

15cm

Explanation:

Focal length of convex lens = +20cm  (using sign convention)

Focal length of concave lens= -5cm (using sign convention)

So, the Focal length of the combination =  

Focal length of convex lens + Focal length of concave lens

= 20 + (-5) = 20-5 = 15cm