- Refraction of light: a term that expresses the change in the path of light when it travels from one transparent medium to another, such as: water and air, oil and glass, ..etc. - A material that contains more particles can refract light significantly, such as: solid materials (such as glass and diamond, for example), while a material that has a smaller number of particles refracts light weakly, such as: liquid materials (such as water and oil, for example) or gaseous materials (such as air, for example). ). The ability of a medium to refract light is called the refractive index (n).