Final answer:
To calculate the power of spectacle lens for a myopic person with glasses 1.75 cm from the eyes, you need to know the person's far point. The calculation involves the lens formula, adjusting for the new glasses-eye distance. Without the specific far point, an exact diopters value cannot be provided.
Step-by-step explanation:
To determine the power of the spectacle lens needed for a nearsighted person when the glasses are 1.75 cm from the eyes, we must consider the far point of the person's vision. In this scenario, the far point of the myopic person is not provided, but we will use the example of a far point of 30.0 cm as a reference, as seen in the related information. The new position of the spectacle lens (1.75 cm instead of 1.50 cm) will affect the calculation of the lens power.
Given that the spectacle lens is 1.75 cm from the eyes, and assuming that the individual's far point remains constant, we would apply the lens formula:
1/f = 1/do + 1/di
,
where f is the focal length, do is the object distance (the far point), and di is the image distance (the corrected near point). Because we want the far point to be effectively at infinity for the person wearing the glasses, we would set the image distance to infinity as well, making the 1/di term equal to zero.
When these adjustments are put into the equation, we can calculate the necessary lens power, which is the inverse of the focal length (in meters), to find the necessary diopters (D).
However, without the specific far point value for this individual with the glasses 1.75 cm from the eyes, we cannot provide an exact number. If we used the far point of 30.0 cm as an example, we would also need to adjust for the new lens-eye distance. The power calculation would require a more complex setup, potentially involving the lens maker's equation to account for the different distances.
In practice, an optometrist would perform a comprehensive examination to determine the correct power for the patient's needs.