People who do very detailed work close up, such as jewellers, often can see objects clearly at much closer distance than the normal 25 cm. (a)What is the power in D of the eyes of a woman who can see an object clearly at a distance of only 7.90 cm? (Assume the lens-to-retina distance is 2.00 cm.) ____________ D (b)What is the size in mm of an image of a 5.00 mm object, such as lettering inside a ring, held at this distance? (Include the sign of the value in your answer.) _____________ mm (c)What would the size of the image be in mm if the object were held at the normal 25.0 cm distance? (Include the sign of the value in your answer.) ________________ mm Solution for the power of lens , do = 7.9 cm di = 2 cm from lens formula 1/f = 1/7.9 + 1/2 f = 1.59 cm Now, power = 100/f Power = 100/1.59 Power = 62.89 D the power of the lens is 62.89 D b) the height of image , hi = - 2*5.00/7.9 hi = - 1.26 mm the height of image is -1.26 mm C) do = 25 cm hi = -2 * 5.0/25 hi = -0.4 mm the height of image is -0.4 mm .

1. People who do very detailed work close up, such as jewellers, often can see objects clearly at
much closer distance than the normal 25 cm.
(a)What is the power in D of the eyes of a woman who can see an object clearly at a distance of
only 7.90 cm? (Assume the lens-to-retina distance is 2.00 cm.)
____________ D
(b)What is the size in mm of an image of a 5.00 mm object, such as lettering inside a ring, held at
this distance? (Include the sign of the value in your answer.)
_____________ mm
(c)What would the size of the image be in mm if the object were held at the normal 25.0 cm
distance? (Include the sign of the value in your answer.)
________________ mm
Solution
for the power of lens ,
do = 7.9 cm
di = 2 cm
from lens formula
1/f = 1/7.9 + 1/2
f = 1.59 cm
Now, power = 100/f
Power = 100/1.59

2. Power = 62.89 D
the power of the lens is 62.89 D
b)
the height of image , hi = - 2*5.00/7.9
hi = - 1.26 mm
the height of image is -1.26 mm
C)
do = 25 cm
hi = -2 * 5.0/25
hi = -0.4 mm
the height of image is -0.4 mm