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.
−50 D
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C.
25 D
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D.
−0.5 D
Correct Answer:
B. −50 D
Explanation:
To determine the power of a lens, you use the formula P = 1/f, where P represents power in diopters (D) and f is the focal length measured in meters. Since the provided focal length is -2 cm, it must first be converted to meters by dividing by 100, resulting in -0.02 m. Applying the formula, P = 1 / (-0.02), which equals -50 D. The negative sign confirms that the lens is concave, as these lenses are diverging and characterized by negative focal lengths and power values.
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