How to hide glass
How to hide glass from prying eyes
- 3 glasses;
- 3 glass rods;
- glass test tube;
- vegetable oil.
Fill the first glass with water, the second glass half with water and half with vegetable oil, and the third with just vegetable oil. Put a glass rod into each glass. Note that the rod disappears in the oil!
Refractive index is a property characterizing how quickly light spreads through a given medium. Each medium – air, water, oil, and glass – has its own refractive index, contingent on the medium's nature and the properties of light. We can see transparent objects because they distort or reflect light in some capacity and thus “appear.” The greater the difference between the refractive indices of light in different media, the higher the distortion. Glass disappears in oil because the two have very similar refractive indices (1.47 and 1.52), meaning that light remains almost undistorted at the border between the oil and the glass. Water’s refractive index (1.33) is significantly lower than that of glass, and thus the glass rod is visible in water.