A concave lens has a focal length of −2 cm. What is its power?
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A.
−0.5 D
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B.
25 D
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C.
−50 D
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D.
0.5 D
Correct Answer:
C. −50 D
Explanation:
The power of a lens is defined as the reciprocal of its focal length when measured in meters (P = 1/f). For a concave lens, the focal length is considered negative. Given: Focal length (f) = -2 cm = -0.02 m Calculation: P = 1 / -0.02 m P = -50 D Therefore, the power of the lens is -50 Dioptres. The correct option is C.
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