A convex lens of 40 cm focal length is combined with a concave lens of focal length 25 cm. The power of combination is:

Question

A convex lens of 40 cm focal length is combined with a concave lens of focal length 25 cm. The power of combination is: (A) -1.5 D (B) -6.5 D (C) +6.6 D (D) +6.5 D

Tardigrade Admin · Accepted Answer

Power of combination is given by P=(1/f1)+(1/f2) Here, f1=40 cm=0.4 m for convex, f2=-25 cm=0.25 m for concave =(1/0.40)+(1/-0.25)=2.5 D-4D=-1.5D

Q. A convex lens of 40 cm focal length is combined with a concave lens of focal length 25 cm. The power of combination is:

-1.5 D

-6.5 D

+6.6 D

+6.5 D

Power of combination is given by $P = \frac{1}{f _{1}} + \frac{1}{f _{2}}$ Here, $f_{1} = 40 c m = 0.4 m$ for convex, $f_{2} = - 25 c m = 0.25 m$ for concave $= \frac{1}{0.40} + \frac{1}{- 0.25} = 2.5 D - 4 D = - 1.5 D$

Q. A convex lens of 40 cm focal length is combined with a concave lens of focal length 25 cm. The power of combination is:

-1.5 D

-6.5 D

+6.6 D

+6.5 D

Power of combination is given by P=f1​1​+f2​1​ Here, f1​=40cm=0.4m for convex, f2​=−25cm=0.25m for concave =0.401​+−0.251​=2.5D−4D=−1.5D

Power of combination is given by $P = \frac{1}{f _{1}} + \frac{1}{f _{2}}$ Here, $f_{1} = 40 c m = 0.4 m$ for convex, $f_{2} = - 25 c m = 0.25 m$ for concave $= \frac{1}{0.40} + \frac{1}{- 0.25} = 2.5 D - 4 D = - 1.5 D$