A myopic person has a power of - 1.25 Dioptre. What is the focal length and nature of his lens ?

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Q: 34 (CDS-I/2016)
A myopic person has a power of -
1.25 Dioptre. What is the focal length and nature of his lens ?

question_subject: 

Science

question_exam: 

CDS-I

stats: 

0,13,39,7,17,15,13

keywords: 

{'focal length': [1, 0, 5, 7], 'convex lens': [0, 0, 0, 4], 'concave lens': [0, 1, 6, 5], 'lens': [0, 0, 0, 1], 'myopic person': [0, 0, 0, 2], 'cm': [2, 0, 7, 20], 'power': [24, 3, 21, 61]}

The correct answer is option 4: 80 cm and concave lens.

In optometry, myopia refers to nearsightedness, where distant objects appear blurry. The power of a lens is measured in diopters (D). A negative power indicates a concave lens, which is used to correct for myopia.

To determine the focal length of the lens, we use the formula:

Focal Length (f) = 1 / Power (P)

The power of a lens in diopters (P) is given as -1.25 D in this question.

Using the formula, we can calculate the focal length as:

f = 1 / (-1.25) = -0.8 m = -80 cm

Hence, the focal length of the lens is -80 cm or 80 cm (when we ignore the negative sign).

Since a negative focal length indicates a concave lens, the nature of the lens is concave.

Therefore, option 4, which states 80 cm and concave lens, is the correct answer.