Final answer:
The power of spectacle lenses needed for farsightedness or nearsightedness depends on shifting the image to the normal range of vision, with diverging lenses for nearsightedness and converging lenses for farsightedness.
Step-by-step explanation:
To correct the vision of a farsighted person whose near point is 1.00 m to see an object clearly that is 25.0 cm away, and considering that the spectacle lens is held 1.50 cm away from the eye, we need to calculate the lens power required to shift the image from the near point to the normal near point (25.0 cm in normal vision). A similar approach is used for calculating the lens power needed for a nearsighted person whose far point is 30.0 cm, also considering the spectacle lens being 1.50 cm away from the eye. In the case of nearsightedness, a diverging spectacle lens is used because the nearsighted eye over converges light rays. The spectacle lens creates an image at or within the far point range, improving the clarity of vision for the nearsighted person.
When using eyeglasses or looking through them backwards and forward, they behave as thin lenses, which follow the principles of lens optics regarding convergence and divergence of light rays. For individuals with lens-to-retina distances smaller than 2 cm, corrective lenses are essential for clear vision. For these individuals, the glasses usually consist of converging lenses if they are farsighted, and diverging lenses if they are nearsighted, to correct their respective visual impairments.