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Question

For general problem-solving tips and strategies for this topic, you may want to view a Video Tutor Solution of Using a lens as a magnifier.

Part A

What power lens should he use as a magnifier to see clearly at a distance of 15 cm without wearing his glasses?

Express your answer using two significant figures.

You may want to review ( pages 606 - 608) .

For general problem-solving tips and strategies for this topic, you may want to view a Video Tutor Solution of Using a lens as a magnifier.

Part A

What power lens should he use as a magnifier to see clearly at a distance of 15 cm without wearing his glasses?

Express your answer using two significant figures.

Explanation / Answer

Take size of the eyeball to be constant and = v

Let the eye lens focal length = f

Magnifier focal length = Fm ( and magnifier held close to eye )

Then the focal length of the combination is given by 1/ f combination (1/fc ) = 1/f + 1/Fm

At 40 cm

1/f = 1/40 + 1/v

At 15 cm

1/fc = 1/15 + 1/v

1/fc = 1/15 + 1/f – 1/40

1/fc – 1/f = 1/24

1/f + 1/Fm – 1/f = 1/24

1/Fm = 1/24

Fm = 24 cm ( that is the answer since power = 1/ f(in metres) = 1/0.24 = 4.16 = 4.16 D )

P =4.16 D

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