Question

Without glasses, your Uncle Albert can see things clearly only if they are between 20 cm and 160 cm from his eyes.

Part A

What power eyeglass lens will correct your uncle's myopia? Assume the lenses will sit 2.0 cm from his eyes.

Express your answer using two significant figures. I got the answer and it is refractive power = -0.63 diopters

but I cant figure out part B

Part B

What is your uncle's near point when wearing these glasses?

Express your answer using two significant figures. d0 = ___________ cm

Answer 1

Given data:

Far point, v = -160 cm
Object distance, u = infinity
Apply the lens formula,
1/f = 1/v – 1/u

Substitute numerical values
1/f = - 1/160 – 1/(infinity)
1/f = -1/160 – 0
f = - 160 cm = 1.6 m
Power = 1/f =- 0.625

Round off the number to 2 significant digits

Power = 0.63 diaptor

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In this case, eye glasses worn 2 cm from eye.

For clear view of perception object should be at 25 cm from eye

Use lens equation

P = 1 /f = 100 [ 1 / - (do - 2 ) ] + 1 / ( 25 - 2. 0 ) ]

- 0.625 = 100 [ 1 / - (do - 2 ) ] + 1 / ( 25 - 2.0 ) ]

- (do - 2 ) = 26.86 cm

do = 24.86 cm

In two significant digits do = 25 cm