Question

An optician prescribes spectacles to a patient
with a combination of convex dens of focal length
40cm & concave lens of focal length 25cm.
Then the power of the spectacles is.
a) -6.50
b) -1.5D.
c) 1.5D
d) 6.5D.​

Answer 1

Answer:

(b.)

Step-by-step explanation:

Let the power of the convex lens be

P1=10040

=2.5D

Let the power of the concave lens be

P2=10025

=−4D

P=P1+P2

=2.5−4.0

=−1.5D