A nearsighted person with a far point of 15 cm wants to read highway signs in th

Question

A nearsighted person with a far point of 15 cm wants to read highway signs in the far distance(assume infinity).What power of glasses are needed, assuming an eye-lens distance of 1.5 cm, to correct their vision? An amateur astronomer has a basic telescope with which to view the moon in her backyard. a. If she wants to magnify the moon by 12x, what focal length eyepiece should she choose if the objective lens has a focal length of 0.6m? b. How long would her telescope have to be in order to accommodate these two lenses?

Explanation / Answer

Q-3 ) Answer

Given Data:-

v = -15 cm , u =-1.5 cm

we have to find the power of glasses.

we know that the power of glass =1/f

f is the focal length. so we have to calculate the focal length first.

use below formula

1/f = 1/v -1/u

1/f = -1/15 - (-1/1.5)

f = 1.66 cm = 0.0166 m

now find the power of glass = 1/f = 1/0.0166 = +60D

A glass having power of +60D can be used to correct the vission.

Q-4) Answer:-

Given Data:-

m = 12x

fobj = 0.6 m

a) we have to find the focal length of eyepeice feye.

We can find it by using formula.

m = focal length of eyepiece / objective focal length

rewrite the formula for focal length of eyepiece.

focal length of eyepiece. = Objective focal length* m

= 0.6 *12

=7.2 m (Answer)

b) we have to calculate the accomodation .

Aoc = M2*U

first find the U =1/ u = 1/0.6

Aoc = 122*1.66 = 239.04

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