The index of refraction of a material does not depend on the angle at which light strikes its surface (the angle of incidence). The index of refraction is a fundamental optical property of the material itself.
Understanding the Index of Refraction
The index of refraction ($n$) is a dimensionless number that describes how fast light travels through a medium. It is defined as the ratio of the speed of light in a vacuum ($c$) to the speed of light in the medium ($v$): $n = c/v$. Different materials, like air, water, or glass, have different indices of refraction because light travels at different speeds through them. This property is intrinsic to the material under specific conditions (like temperature and wavelength), not dependent on how the light enters it.
The Role of Snell's Law
The relationship between the angles of incidence and refraction when light passes from one medium to another is described by Snell's Law (Formula 1 in the reference). While the full formula isn't provided, Snell's Law establishes a crucial link: it relates the angles of the light rays to the indices of refraction of the two media involved.
Snell's Law shows how the angle of refraction depends on the angle of incidence and the indices of refraction of the two materials. It does not state that the indices of refraction change with the angle of incidence.
Relationship Between Angles and Indices (Based on Reference)
The provided information clarifies how the indices of refraction influence the angles:
- When n(2) is greater than n(1) (e.g., light moving from air into glass), the angle of refraction is always smaller than the angle of incidence. This means the light ray bends towards the normal (an imaginary line perpendicular to the surface).
- When the two refractive indices are equal (n(1) = n(2)), then the light is passed through without refraction. The light ray continues in a straight line, and the angle of refraction equals the angle of incidence.
This confirms that the difference or equality between the indices of refraction ($n_1$ and $n_2$) dictates how the angles of incidence and refraction relate, not the other way around. The indices $n_1$ and $n_2$ are properties of Medium 1 and Medium 2, respectively, and remain constant for a given wavelength and conditions, regardless of the angle $\theta_1$ at which the light arrives.
In summary, while the angle of incidence plays a key role in determining the angle of refraction via Snell's Law, it does not affect the index of refraction of the material itself.
