Question

the focal length of the combination of convex lens of power 1d and concave lens of power -1.5d is​

Answer 1

Answer:

+1D+(-1.5)D

⇒ 1D-1.5D= -0.5D

Since the sign is negative (-), therefore the nature of lens is concave

Hope this helps  :D

Answer 2

Given:-

• Power of Convex lens (P₁) = 1 d

• Power of Concave lens (P₂) = -1.5d

To Find:-

• Focal length of the combination (F).

Solution:-

As we know that

Power is defined as the reciprocal of its focal length.

Firstly we calculate the power of combination of lens

→ P = P¹ + P₂

Substitute the value we get

→ P = 1 + (-1.5)

→ P = 1-1.5

→ P = -0.5D

Now Calculating the Focal length of combination of lens

→ P = 1/F

Substitute the value we get

→ P = 1/F

→ -0.5 = 1/F

→ -1/0.5 = F

→ F = -2cm

∴ The focal length of the combination of lens is -2cm or 2/100 = 0.02m