Question

Two thin lenses of power + 2.5 D and - 0.5 D are placed in contact. Find the power and focal length of the lens combination. Also calculate the focal length of the combination.

Answer 1

Answer:

Explanation:

Solution,

Here, we have,

Power one of lens = P₁ = + 2.5 D

Power two of lens = P₂ = - 0.5 D

To Find,

Power and focal length

We know that,

Power combination = P₁ + P₂

= + 2.5 + (- 0.5)

= 2.5 - 0.5

= 2 D

Hence, the power is 2 D.

Now, Focal length,

We know that,

Power = 1/focal length

⇒ 2 = 1/f

⇒ 2/1 = f

⇒ f = 2 m

Hence, the focal length is 2 m.

Answer 2

Answer:

0.5 m

Explanation:

power combination= power 1 + power 2

= 2.5 + (-0.5)

= 2 D

we know,

power =

$\frac{1}{focal \: length}$

focal length = 1/2

= 0.5meter

= 50 cm