Question

9. Doctor advised to use -4D lens. find the
focal length of lens in cm and also in metre. What can you infer about
nature of lens? ?​

Answer 1

Answer:

curvature is found to be equal to twice the focal length. ... (You can also find it out by obtaining ... A doctor has prescribed a corrective lens of power + 1.5 D. Find the focal length of the.

Shubham Kmr Yash

Answer 2

Answer:

The focal length of the lens is 0.25 m i. e. 25 cm.

The nature of the lens is concave lens.

Explanation:

Given data:

Power of lens = - 4 D

To find:

Focal length ( f ) of the lens

Solution:

We know that,

$\displaystyle\pink{\sf\:Power\:of\:lens\:=\:\dfrac{1}{Focal\:length\:(\:m\:)}}$

$\implies\sf\:P\:=\:\dfrac{1}{f}$

$\implies\sf\:-\:4\:=\:\dfrac{1}{f}$

$\implies\sf\:f\:=\:-\:\dfrac{1}{4}$

$\implies\boxed{\red{\sf\:f\:=\:0.25\:m}}$

Now, we know that,

$\sf\:1\:m\:=\:100\:cm$

$\implies\sf\:f\:=\:0.25\:m$

$\implies\sf\:f\:=\:100\:\times\:0.25\:cm$

$\implies\boxed{\red{\sf\:f\:=\:25\:cm}}$

The focal length of the lens is 0.25 m i. e. 25 cm.

$\rule{200}{1}$

The power of the lens is - 4 D.

It is negative.

Hence, it shows that, the lens is a concave lens.

The nature of the lens is concave lens.

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