Have you ever had such an experience? Lost the key to the locker in the swimming pool and found it at the bottom of the shallow pool. When you reach into the water and want to pick it up, it's easy to pick up the wrong place.
This phenomenon can be explained by the refraction of light at the boundary of two different media. If you are in a swimming pool full of salt water, the image location of the key will be moved more. A kind of
Light moves at different speeds in materials of different densities. In vacuum, it moves at 299792458 M / s, while in water, it only reaches 225000000 M / s. A kind of
If a beam of light with a fixed wavelength reaches the boundary of two media at a fixed angle, the angle of the light will change according to the refractive index of the media. Snell's law can describe this phenomenon: n 1 · sin α 1 = N 2 · sin α 2, α 1 is angle a, α 2 is angle B
When the condition is stable and the medium is known, the formula can be used to calculate the refractive index of the second unknown medium. The angle of incidence and the angle of refraction can be measured. It is a simple mathematical problem to know the refractive index of one material (using prism refractometer), adjust the formula and get the refractive index of unknown material.
The measurement of refractive index depends on the temperature and wavelength of light. It can be used to provide the composition information of the pure substance, but the exact composition cannot be provided. The refractive index of water is 1.33 at 20 ℃, while that of ice is 1.31.
The refractive index of purified water with added sugar will change, which depends on the amount of added sugar. The refractive index of pure water with salt also changes, which is related to the concentration of salt water. A kind of
So if the refractive index of pure water is not 1.33 at 20 ℃, it has been "polluted" by other substances.
Generally, it is fast and reliable to determine the purity of a substance by its refractive index. Therefore, if the sunflower oil is added with other cheap oil or sugar in jam, it can be easily detected in the production process according to this principle. A kind of
Another example is that cyclohexane has the same refractive index as 52.9% sugar solution at 20 ℃. Therefore, unless the composition of the substance is known accurately, it is impossible to judge the condition of the composite or the composition of the mixture according to the refractive index. A kind of
Temperature is one of the most important factors affecting the refractive index. Each substance is affected differently by temperature. Chinese style
The temperature correction of Refractometers must always be specific to specific substances, rather than general standards.