Refraction is a phenomenon that occurs when light waves travel from one medium to another and change direction. It happens because the speed of light is different in different substances. When light passes through a medium with a different optical density (refractive index), such as air to water or air to glass, it bends or changes its direction.

Key points about refraction:

1. The Refractive Index: The refractive index of a substance is a measure of how much it slows down light compared to its speed in a vacuum. It is typically represented by the symbol “n.” The refractive index determines the amount of bending or deviation that occurs when light travels from one medium to another.
2. Snell’s Law: Snell’s law describes the relationship between the incident angle of light, the refracted angle, and the refractive indices of the two media. It states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is equal to the ratio of the refractive indices of the two media.
3. Angle of Incidence and Refraction: When light passes from a less dense medium (lower refractive index) to a more dense medium (higher refractive index), it bends towards the normal, an imaginary line perpendicular to the surface of the interface between the two media. The angle between the incident light ray and the normal is called the angle of incidence. Similarly, the angle between the refracted light ray and the normal is called the angle of refraction.
4. Refraction and Change in Speed: When light passes through a medium with a higher refractive index, such as from air to water or air to glass, it slows down, and as a result, its wavelength becomes shorter. The change in speed causes the light waves to bend at the interface.
5. Total Internal Reflection: Total internal reflection occurs when the angle of incidence is larger than the critical angle for a given pair of media. In this case, no refraction occurs, and all of the light is reflected back into the original medium. Total internal reflection is the principle behind phenomena like fiber optics and mirages.
6. Practical Applications: Refraction has practical applications in various fields. Lenses, such as those in eyeglasses or cameras, use refraction to focus light and correct vision or capture images. Prisms utilize refraction to disperse light into its component colors. Optical fibers use total internal reflection to transmit light signals over long distances for communication purposes.

Refraction is an important phenomenon that plays a crucial role in our understanding of light and its behavior as it interacts with different materials. It has both scientific and practical applications, making it a significant concept in physics and optics.