Question

Suppose you are myopic (nearsighted). You can clearly focus on objects that are as far away as 52.5 cm away. You can clearly focus on objects which are as close as 17.2 cm from your eyes, but no closer. The purpose of glasses would be to make objects that are far away appear to be at your far point. What would be the refractive power (in diopters - do not enter units) for your prescription?If your glasses make distant objects appear to be at your far point, then any object that is closer to you will appear even closer than it really is. What is the closest distance from your face at which you could hold a book and still be able to see it clearly while wearing your glasses?

Answer 1

Step-by-step explanation:

Image of distant object will be made at far point or at 52.5 so

object distance u = infinity

image distance v = - 52.5 cm

focal length required = f

Lens formula

1 / v - 1 / u = 1 / f

1 / - 52.5 - 0 = 1 / f

f = -52.5 cm

= -.525 m

Power P = 1 / f = - 1 / .525

= - 1.90

now , for eye with glass we shall find new near point .

v = ?

u = - 17.2 cm

f = - 52.5 cm

1 / v - 1 / u = 1 / f

1 / v + 1 / 17.2 = - 1 / 52.5

1 / v = - 1 / 17.2 - 1 / 52.5

= - .05813 - .019

= - .07713

u = - 12.96 cm

so new near point will be 12.96 cm