Question

Mary's glasses have +4.4D converging lenses. This gives her a near point of 20cm. What is the location of her near point when she is not wearing her glasses?

Express your answer with the appropriate units.

Answer 1

The position of near point is 1.68 m.

Step-by-step explanation:

Given that,

Power = + 4.4 D

Object distance = 20 cm

We need to calculate the focal length

Using formula of power

`P =(1)/(f)`

`f=(1)/(P)`

`f=(1)/(4.4)`

`f=0.227\ m`

We need to calculate the image distance

Using formula of lens

`(1)/(f)=(1)/(v)-(1)/(u)`

`(1)/(v)=(1)/(f)+(1)/(u)`

Put the value into the formula

`(1)/(v)=(1)/(0.227)-(1)/(0.20)`

`(1)/(v)=-(135)/(227)`

`v=-1.68\ m`

Hence, The position of near point is 1.68 m.