Final answer:
Refractive indices are not physical constants as they vary with light wavelength, medium, and conditions; this variation is vital for applications like fiber optics. Refraction is essential in fiber optic cables for signal transmission.
Step-by-step explanation:
Refractive indices are not physical constants because they vary with the wavelength of light, temperature, and the medium through which the light is traveling. The refractive index for a material is defined as the ratio of the speed of light in a vacuum to the speed of light in that material.
From this definition, it's clear that because the speed of light can vary in different media and conditions, the refractive index can also change. For example, refractive indices are different for different wavelengths which leads to dispersion seen as colors produced by a prism.
In the context of the eye, the refractive index varies throughout the lens and is vital for proper image formation on the retina. It is important to note that while gases typically have refractive indices close to 1, they are taken as exactly 1 for general calculations unless high precision is necessary.
The statement that refraction is useful in fiber optic cables for transmitting signals is true. Fiber optic cables work on the principle of total internal reflection, which relies on the refraction of light at the interface between two materials with different refractive indices.