. A nearsighted person has near and far points of 10.0 cm and 20.0 cm, respectiv

Question

. A nearsighted person has near and far points of 10.0 cm and 20.0 cm, respectively, when she does not wear any corrective lenses. Her contact lenses have a power equal to 4.75 diopters, which is not strong enough to completely correct her vision. (a) Calculate the farthest distance from her eyes that an object can be placed and still be in focus when she is wearing the contacts. Explain clearly. (Hint: the image of this object must be formed at 20.0 cm from her eyes.) (b) Calculate the closest distance she can hold a book and still be able to read it, when she is wearing the contacts. Explain clearly. Notice that wearing the contacts makes it harder to see objects up close.

Explanation / Answer

b)

Focal length = (-1/D) m or 100/475 m or 21.02 cm.

Lens should be diverging object distance is considered +ve and diverging lens is supposed to have + ve focal length.

So

near point will now shift to say V given by

1/V - 1/4.35 = 0.047 or 1/V = 0.277

V = 3.61 cm
a)

Similarl far point will be at V2 given by
1/V2 = [{1000+(475*10)}/(100*10)] = 4.85 cm

v2 =0.206 cm

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