If you could just explain how to do one of these, that would be fantastic! I\'m

Question

If you could just explain how to do one of these, that would be fantastic! I'm not sure how to set it up...


A machinist with normal vision has a near point at 25 cm. The machinist wears eyeglasses in order to do close work. The power of the lenses is +4.25 diopters. With these eyeglasses, the near point of the machinist, in cm, is closest to:

A myopic girl wears eyeglasses that allow her to have clear distant vision. The power of the lenses of her eyeglasses is -3.00 diopters. Without eyeglasses, the far point of the girl is closest to:

A farsighted boy has a near point at 2.0 m and requires eyeglasses to correct his vision. Corrective lenses are available in increments in power of 0.25 diopters. The eyeglasses should have lenses of the lowest power for which the near point is no further than 25 cm. The boy borrows eyeglasses that have a power of +2.75 diopters. With these eyeglasses, the near point of the boy, in cm, is closest to:

Explanation / Answer

Final image is at v = -25 cm Near point is at u =? Focal length, f =100/4.25 = 23.529cm L:ens eqn:             1/v + 1/u = 1/f           1/u = 1/f - 1/v                 = 1/23.529 + 1/25           u =12.121 cm

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