Question

The power of a convex lens is 5d and the power of a concave lens is 2d.what is the combination of these lenses when placed togather

Answer 1

Given that -

The power of a convex lens is 5d and the power of a concave lens is 2d.

To Find-

Combination of these lenses when placed togather.

Solution-

We know that power of lens of concave lens is in negative and has negative focal length & that of convex lens is positive and has positive focal length.

So we can write it like-

• Power of concave lens = +2d
• Power of convex lens = -5d

Let's denote the power of concave lens by P1 and convex lens by P2.

To find the power combination of both concave lens and convex lens, we have to add their powers i.e.

P = P1 + P2

Substitute their values,

→ P = +2d + (-5d)

→ P = +2d - 5d

→ P = -3d

Therefore, the power of combination of both concave and convex lens is -3d.

Answer 2

Given that,

• Power of a given convex lens = 5 D
• Power of a given concave lens = 2 D

→ Combination of these lenses when placed together = ?

As we know,

◘ Convex lens has a negative power.

◘ Concave lens has a positive power.

So, we finally get :-

• Power of the convex lens = -5 D
• Power of the concave lens = 2 D

$\rule{190}3$

Now,

We know Power of combination of lenses :-

→ Power of Combination(P) = Power of the convex lens(P') + Power of the concave lens(P'')

⇒P = (-5) + 2

⇒P = -3 D

Therefore, the power of lenses when placed together is -3 D.