Certified Ophthalmic Assistant Practice Exam

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What is the power of a lens with a focal length of 2 meters?

2D
1D
0.5D
0.25D

The correct answer is: 0.5D

The power of a lens is calculated using the formula: power (P) in diopters (D) is equal to 1 divided by the focal length (f) in meters. Thus, if the focal length of the lens is 2 meters, the calculation would be: P = 1 / f = 1 / 2 = 0.5 D. This means that the lens has a power of 0.5 diopters, which indicates it is a weak converging lens. The power is inversely related to the focal length; longer focal lengths yield lower power values. Hence, the correct answer is that the power is 0.5D.