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Question number 5​

Answer 1

Answer:

Given:

The person needs - 5.5 D for correcting his distant vision. He also needs +1.5 D for. correcting his near vision.

To find:

Focal length of lens for correcting

• Distant vision
• Near vision.

Concept:

Power of lens is actually the capability of lens to deviate the light rays.

It is the reciprocal of Focal length .

P = 1/f

Calculation:

For distant vision:

P = 1/f

=> - 5.5 = 1/f

=> f = - 1/(5.5)

=> f = - 0.1818 metres

=> f = - 18.18 cm.

Negative sign refers to concave lens.

For near vision:

P = 1/f

=> +1.5 = 1/f

=> f = 1/(1.5)

=> f = 0.677 m

=> f = 67.7 cm.

Positive sign refers to convex lens