Question

name the type of the lens if its power is 20D find the focal length of this lens​

Answer 1

Answer:

The positive value of focal length shows that the lens is convex lens.

Explanation:

We are given that:

• Power of lens = 20 D
• To Find: Focal length = ?

Solution:

The focal length of the lens can be found by using the focal length power formula.

f = 1 / power

f = 1 / D

f = 1/ 20

f = 0.05 cm

As the focal length is positive the lens is convex lens.

Answer 2

The correct answer is "Convex lens". The further explanation is given below.

Explanation:

As we know, the given power is "2D".

We know that the focal length will be:

⇒  $f=\frac{1}{power}$

On putting the value, we get

⇒     $=\frac{1}{20}$

⇒     $=0.05 \ cm$

The lens would be convex, but since focal length becomes positive.