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.

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CarliReifsteck CarliReifsteck · Answer 1 · 2019-09-16T14:57:17+02:00

Answer:

The position of near point is 1.68 m.

Explanation:

Given that,

Power = + 4.4 D

Object distance = 20 cm

We need to calculate the focal length

Using formula of power

[tex]P =\dfrac{1}{f}[/tex]

[tex]f=\dfrac{1}{P}[/tex]

[tex]f=\dfrac{1}{4.4}[/tex]

[tex]f=0.227\ m[/tex]

We need to calculate the image distance

Using formula of lens

[tex]\dfrac{1}{f}=\dfrac{1}{v}-\dfrac{1}{u}[/tex]

[tex]\dfrac{1}{v}=\dfrac{1}{f}+\dfrac{1}{u}[/tex]

Put the value into the formula

[tex]\dfrac{1}{v}=\dfrac{1}{0.227}-\dfrac{1}{0.20}[/tex]

[tex]\dfrac{1}{v}=-\dfrac{135}{227}[/tex]

[tex]v=-1.68\ m[/tex]

Hence, The position of near point is 1.68 m.