How can you bend a beam of light?
Attention! Do not point the laser at your eyes! It may cause injury! Use eye protection!
- laser pointer;
- vegetable oil;
Use a spray gun or smoke to highlight the beam of light and make the refraction easier to observe. To achieve complete internal reflection, gently pour some vegetable oil over some water. In order to visibly bend the light, make a saturated salt solution (recommended ratio 350g salt : 1L water. Pour fresh water into the aquarium, then use a syringe with a tube to carefully add the salt solution to the bottom. Point the laser beam at an angle to the side wall of the vessel and you will see something amazing! By adjusting the angle of incidence of light, you can bend the beam down completely.
Different light-transmitting media have different refractive indices. A medium’s refractive index indicates how the speed of light in vacuum relates to the speed of light in said medium. The higher the medium's refractive index, the slower light travels through it. When a ray of light crosses the boundary between two media, it is partially refracted and reflected. Moreover, the angle of incidence is always equal to the angle of reflection. The refraction of light is a phenomenon in which a ray changes directions when transitioning from one medium to another. If there is no refracted beam, then the light is reflected completely. A medium is called “optically homogeneous” if its refractive index is the same across all points, which means that light propagates linearly through it. Accordingly, a medium is “optically inhomogeneous” if the refractive index varies from point to point, which causes nonlinear propagation of light. A saturated salt solution and freshwater have different refractive indices: the refractive index of a salt solution is greater than that of freshwater. Due to mixing and diffusion, after a while, a layer of optically inhomogeneous liquid forms at the boundary between them. When entering the optically inhomogeneous liquid layer, the light beam is bent, bending towards increasing values in refractive index.