Question

a myopic person has been using spectacles of power -1dioptre . during his old age he needs separate glasses of power +2 dioptre. explain what may happen? ​

Answer 1

Answer:

myopic personhas been using spectales of power 1 diotre because they are unable to see things that are kept at large distance as their retina gets damaged

Answer 2

GiveN :

It is given that the person is using the spectacles with Power -1.0 dioptre, So as a result focal length is unknown.

We know that,

$\longrightarrow\sf D = \dfrac{100}{F}$

where D is diopters and F is the focal length in centimeters.

Substituting the values,

$\longrightarrow\sf F = \dfrac{100}{D}$

$\longrightarrow\sf F = \dfrac{100}{1.0}$

$\longrightarrow{ \boxed{\sf {F = 100 \: cm}}}$

As the far point is at 100 cm. The near point of the eye sight might be at 25 cm.

As a result to see objects between 25 cm & 100 cm one should've the ability of accommodation of their eye lens.

Naturally, this ability is lost at old age of a person. So, we can conclude that the near point of the eye may go back to 50 cm.

Now, let's find out the total Power.

Accordingly,

• Object distance, u = -25 cm

• Image distance, v = -50 cm

And we've to find the focal length in this case.

We know that,

$\longrightarrow\sf \dfrac{1}{f} = \dfrac{1}{v} - \dfrac{1}{u}$

$\longrightarrow\sf \dfrac{1}{f} = \dfrac{1}{ - 50} - \dfrac{1}{ - 25}$

$\longrightarrow\sf \dfrac{1}{f} = \dfrac{1}{ - 50} - \dfrac{1}{ - 25}$

$\longrightarrow\sf \dfrac{1}{f} = \dfrac{ - 1}{ 50} + \dfrac{1}{ 25}$

$\longrightarrow\sf \dfrac{1}{f} = \dfrac{ - 1 + 2}{ 50}$

$\longrightarrow\sf \dfrac{1}{f} = \dfrac{ 1}{ 50}$

$\longrightarrow \large{ \boxed{\frak{f = 50 \: cm}}}$

Now, we know that,

$\longrightarrow\sf P = \dfrac{100}{f}$

$\longrightarrow\sf P = \dfrac{100}{50}$

$\longrightarrow \large{ \boxed{\frak{ P = + 2 \: dioptre}}}$

Hence Solved.