A farsighted person has a near point that is 48.0 cm from her eyes. She wears ey

Question

A farsighted person has a near point that is 48.0 cm from her eyes. She wears eyeglasses that are designed to enable her to read a newspaper held at a distance of 22.0 cm from her eyes. Find the focal length of the eyeglasses, assuming each of the following.

If you cant read this here is the question : A farsighted person has a near point that is 48.0 cm from her eyes. She wears eyeglasses that are designed to enable her to read a newspaper held at a distance of 22.0 cm from her eyes. Find the focal length of the eyeglasses, assuming each of the following. (a) that they are worn 2.0 cm from the eyes cm (b) that they are worn 3.0 cm from the eyes cm

Explanation / Answer

Use 1/f = 1/s + 1/s' where s is the object distance = 24.0 - 2.0cm = 22.cm and s' is (-48 - 2.0) = -46.0cm

The negative is because the image is virtual

a) 1/f = 1/22 + 1/-46 => f = 42.1666 cm

b ) Now we have 1/f = 1/21 + 1/-45 => f = 39.37 cm

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