Final answer:
The term for the minimum angle at which a light ray is totally internally reflected and cannot pass into the surrounding medium is called the critical angle. This angle depends on the indices of refraction of the materials involved and varies for different wavelengths of light.
Step-by-step explanation:
Understanding the Critical Angle in Optics
The concept in question is known as the critical angle, which is the minimum angle of incidence above which total internal reflection occurs when light travels from a medium with a higher index of refraction to one with a lower index of refraction. The critical angle varies for different materials because it depends on the indices of refraction of the two media. In the context provided, different wavelengths (colours) of light such as red and violet light will have different critical angles when passing from diamond to air, which demonstrates that the critical angle is dependent not only on the material properties but also on the light's wavelength.
Different materials have different indices of refraction, and thus their critical angles will vary. For example, the critical angle for light going from water to air is 48.6°, from diamond to air is 24.4°, and from flint glass to crown glass is 66.3°. These differences in critical angles are what cause phenomena like total internal reflection, which has practical applications in fiber optics and other fields.
If light hits the interface at an angle greater than the critical angle, it will not pass into the second medium but instead will be totally reflected back into the first medium. This concept has many applications, including the creation of perfectly reflective surfaces without the need for traditional mirror coatings.