1) A farsighted person has a nearpoint of 55.0 cm from her eyes. She wants glass
ID: 2201181 • Letter: 1
Question
1) A farsighted person has a nearpoint of 55.0 cm from her eyes. She wants glasses that will let her see objects at a distance of only 25.0 cm from her eyes. Determine the focal length of the glasses needed if the glasses are 2.0 cm and 3.0 cm from her eyes. (Remember, a converging lens has a positive focal length and a diverging lens has a negative focal length.)
f2.0 cm=
2)f3.0 cm=
3) A nearsighted person has a farpoint of 490.0 cm from his left eye and 661.0 cm from his right eye. He wants contact lenses that will let him see objects at a great distance. Determine the focal length of the contact lens needed for each eye. (Remember, a converging lens has a positive focal length and a diverging lens has a negative focal length.)
fleft=
4)fright=
Explanation / Answer
) A farsighted person has a nearpoint of 58 cm from her eyes. She wants glasses that will let her see objects at a distance of only 25 cm from her eyes. Determine the focal length of the glasses needed if the glasses are 2 cm and 3 cm from her eyes. (Remember, a converging lens has a positive focal length and a diverging lens has a negative focal length.) f2 cm = cm f3 cm = cm (b) A nearsighted person has a farpoint of 505 cm from his left eye and 639 cm from his right eye. He wants contact lenses that will let him see objects at a great distance. Determine the focal length of the contact lens needed for each eye. (Remember, a converging lens has a positive focal length and a diverging lens has a negative focal length.) fleft = cm fright = cm ) A farsighted person has a nearpoint of 58 cm from her eyes. She wants glasses that will let her see objects at a distance of only 25 cm from her eyes. Determine the focal length of the glasses needed if the glasses are 2 cm and 3 cm from her eyes. To find F2, you need to subtract 2 cm from nearpoint and 25 cm. 1/f = -1/56 + 1/23 1/f= 33/1288 f = 39 :. F2 cm = 39cm To find F3, you need to subtract 3 cm from nearpoint and 25 cm. 1/f = -1/55 + 1/22 1/f= 3/110 f = 36.6 ;. F3 cm = 37cm (b) A nearsighted person has a farpoint of 505 cm from his left eye and 639 cm from his right eye. He wants contact lenses that will let him see objects at a great distance. Determine the focal length of the contact lens needed for each eye. No subtraction is needed to solve for F: For the left eye, farpoint = 505cm 1/f = 1/infinity - 1/505 f = -505 :. F(left eye) = - 505cm For the right eye, farpoint = 639cm 1/f = 1/infinity - 1/639 f = -639 ;. F(right eye) = - 639cm
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