HELP PLEASE! 1) A farsighted person has a nearpoint of 49 cm from her eyes. She
ID: 1460628 • Letter: H
Question
HELP PLEASE!
1)A farsighted person has a nearpoint of 49 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
2)
f3 cm = ?cm
3)
A nearsighted person has a farpoint of 504 cm from his left eye and 649 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
4)
fright = ?cm
Explanation / Answer
1)
case 1: glasses 2 cm from the eye
di = image distance = - (49 - 2) = -47 cm
do = object distance from glass = 25 - 2 = 23 cm
f = focal length
Using the equation
1/di + 1/do = 1/f
1/ (-47) + 1/23 = 1/f
f = 45.04 cm
case 2: glasses 3 cm from the eye
di = image distance = - (49 - 3) = -46 cm
do = object distance from glass = 25 - 3 = 22 cm
f = focal length
Using the equation
1/di + 1/do = 1/f
1/ (-46) + 1/22 = 1/f
f = 42.2 cm
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