光的折射是一个重要的光学现象，当光从一种介质进入另一种光学密度不同的介质时就会发生。当光从空气进入水中时，由于传播速度的改变，光线会向法线方向弯曲。入射光线是进入的光，而折射光线是穿过两种介质界面后弯曲的光。
Snell's Law describes the mathematical relationship governing light refraction. The equation n₁ sin θ₁ equals n₂ sin θ₂, where n represents the refractive index of each medium and θ represents the angles. As we change the incident angle, we can observe how the refracted angle changes according to this law. Different materials have different refractive indices - air is approximately 1.00, water is 1.33, and glass is around 1.50.
The refractive index determines how much light bends when entering a material. Different materials have characteristic refractive indices - vacuum and air are 1.000, water is 1.333, glass is 1.500, and diamond is 2.417. The refractive index relates to light speed through the equation n equals c over v, where c is the speed of light in vacuum and v is the speed in the material. When light enters a denser medium with higher refractive index, it bends toward the normal line.
The critical angle is a special phenomenon that occurs when light travels from a denser medium to a less dense medium. The critical angle formula is theta c equals arcsine of n2 over n1. For glass to air, this gives us 41.8 degrees. When the incident angle is less than the critical angle, refraction occurs normally. However, when the incident angle exceeds the critical angle, total internal reflection occurs instead of refraction.
Light refraction has many practical applications in our daily lives. Optical fibers use total internal reflection to transmit light signals over long distances for communication. Eyeglasses and camera lenses use controlled refraction to focus or diverge light rays for vision correction and imaging. Prisms demonstrate dispersion, where different wavelengths of white light refract at slightly different angles, separating into a spectrum of colors.