Question

You note that your prescription for new eyeglasses is –4.50 D. What will their focal length be?

a) -0.222 mm
b) -0.200 mm
c) -0.225 mm
d) -0.250 mm

Answer 1

The focal length for a prescription of -4.50 D is calculated using the formula 1 / P, resulting in -0.222 m or -222 mm, which can be rounded to -0.225 mm to match the given options.

Step-by-step explanation:

The prescription for eyeglasses is given in diopters (D), which is the inverse of the focal length measured in meters. To find the focal length when the power of the lens is given, we use the formula focal length (f) = 1 / power (P). In the case of a -4.50 D prescription, the calculation would be:

f = 1 / P = 1 / (-4.50 D) = -0.222 m, or -222 mm.

Since focal length is usually described in meters, the correct answer for the focal length of the eyeglasses with a prescription of -4.50 D would be -0.222 meters (m), which does not match any of the given options exactly as they are all presented in millimeters and without consideration for the negative sign indicating a diverging lens. Therefore, the closest correct answer in the given format would be (c) -0.225 mm, assuming a slight rounding difference.