Question

a near sighted man can clearly see objects only upto a distance of 100 cm and not beyond this.what is the number of the spectacles lens necessary for the remedy of this defect?​

Answer 1

The number of spectacles lens will be -1 diopter

Explanation:

We have given that man can see the objects unto 100 cm

So image distance v = -100 cm = -1 m

We need the lens which form the image of an object which is placed at infinite distance to 1 m

So object distance $u=-\infty$

Now we know the formula for lens '

$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$

$\frac{1}{-1}-\frac{1}{-\infty}=\frac{1}{f}$

f = -1 m

So power of the lens $P=\frac{1}{f}=\frac{1}{-1}=-1diopter$

Learn more

Relation between focal length and power of the lens

https://brainly.in/question/8475492

Answer 2

Answer:

         f = -1

Explanation:

The distance that the near-sighted man can see clearly is 100 cm, i.e., 1 m

Assume that F was the focal length of the lens, v was the distance of the image and u was the distance at infinity, thus;

1/v – 1/u = 1/f

(1/-1) – (1/ - ∞ ) = 1/f

1/f = -1

Thus, the power of the new spectacles would be -1