Question

A convex lens of focal length 40 cm is in contact with a concave lens of focal length 25 cm. The power of the combination is
A. `+1.5`
B. `-1.5`
C. `+6.67`
D. `-6.67`

Answer 1

Correct Answer - B
Power of convex lens `P_(1)=(100)/(40)=2.5D`
Power of concave lens `P_(2)=-(100)/(25)=-4D`
Now `P=P_(1)+P_(2)=2.5D-4D=-1.5D`