76.   A woman can read the large print in a newspaper only when it is at a distance of 65 cm or more from her eyes. (a) Is she nearsighted (myopic) or farsighted (hyperopic), and what kind of lens is used in her glasses to correct her eyesight? (b) What should be the refractive power (in diopters) of her glasses (worn 2.0 cm from the eyes), so she can read the newspaper at a distance of 25 cm from her eyes?

 

Since the woman cannot read things close to her she is Farsighted or Hyperopic! So she will need converging lenses.

 

Refractive power is found from

If focal length is in meters, Power will be diopters.

 

So we find the focal length.  Object distance will be 25 cm – 2 cm = 23 cm.  Image distance will be – (65 cm -2 cm = 63 cm) as it needs to be a virtual image.

 

 

 

So power is

 

 

 

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This page last updated on July 7, 2018