Final answer:
The natural near point of a farsighted person prescribed +1.91 diopter lenses is found by using the lens power formula and considering the glasses-eye distance. The calculation leads to a natural near point of approximately 54 cm from the eye.
Step-by-step explanation:
To find the natural near point of a farsighted person prescribed corrective lenses with a power of P= +1.91 diopters, we use the formula for lens power, which is P = 1/f, where f is the focal length in meters.
Since the prescribed glasses are 2 cm away from the eyes, we need to consider this distance when calculating the near point of the individual. The standard near point is 25 cm, but with the glasses, the image has to form at (25 - 2) cm, which is 23 cm from the lenses to be at the standard near point for the eyes.
We convert this distance to meters, it becomes 0.23 m. Hence, f = 0.23 m for the corrective lenses. When we convert the power of the lenses into focal length, we get f = 1/P, which gives us f = 1/1.91 m, or approximately f = 0.524 m. This is the distance from the glasses to the near point of the uncorrected eye. However, we must add the 2 cm (or 0.02 m) glasses-eye distance to find the actual near point distance from the eyes, which gives us 0.524 m + 0.02 m = 0.544 m. Converting this back to centimeters, we get 54.4 cm, which rounds to 54 cm. Therefore, the natural near point is approximately 54 cm from the eye.