The refractive index of ruby is 1.76. What is the meaning of this statement in relation to the speed of light.

Hint: Refractive index depends on a medium with respect to air is defined as the speed of light in air to the speed of light in that material. Therefore, the refractive index of air is 1. Any medium with density greater than that of air will have a higher refractive index or a lower speed of light.

 Complete step-by-step solution
Refractive index of light is given as the ratio of sin of angle of incidence to the sine of angle of refraction. It is given as
 \[\mu = \dfrac{{\sin (i)}}{{\sin (r)}}\]
Where i is the angle of incidence of light
R is the angle of refraction of light
This refractive index can also be written in the form of speed of light as
 \[\mu = \dfrac{c}{v}\]
Where c is the speed of light in vacuum
V is the speed of light in the medium.
As refractive index of ruby is 1.76, it means that speed of light in this medium is reduced by a factor of 1.76 times the original value

 Note: The refractive index of a material can also be written in the form of wavelength of \[\mu = a + \dfrac{b}{{{\lambda ^2}}}\], this equation is known as the cauchy’s equation. However, Cauchy's equation is only valid for visible spectrum of light. It fails when we take into consideration the wavelength of infrared or any other wave.