A farsighted person has a nearpoint of 46 cm from her eyes. She wants glasses th

Question

A farsighted person has a nearpoint of 46 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.)

1. f2 cm =

2. F3cm=

A nearsighted person has a farpoint of 480 cm from his left eye and 642 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.)

3. Fleft=

4. Fright=

Explanation / Answer

a) A farsighted person has a nearpoint of 46 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 = -1/44 + 1/23
1/f= 21/1012
f = 48.19
:. F2 cm = 48.19cm

To find F3, you need to subtract 3 cm from nearpoint and 25 cm.
1/f = -1/43 + 1/22
1/f= 21/946
f = 45
;. F3 cm = 45cm

(b) A nearsighted person has a farpoint of 480 cm from his left eye and 642 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 = 480 cm
1/f = 1/infinity - 1/480
f = -480
:. F(left eye) = - 480cm

For the right eye, farpoint = 642 cm
1/f = 1/infinity - 1/642
f = -642
;. F(right eye) = - 642 cm

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.