Disappearing Glass
Purpose
Demonstrates index matching: when two transparent materials share the same refractive index, light crosses their interface without refraction or reflection, making the boundary invisible. Students see this dramatically as glass tubes vanish or appear when immersed in oil.
Figure 1:
Apparatus tilted to immerse one set of glass tubes in oil. The letters behind the oil-filled vial (right) appear through a simple cylindrical lens — the index-matched tubes are invisible. The exposed tubes in the left vial distort the background.
Figure 2:
Apparatus tilted the other way. Now the left vial's index-matched tubes disappear in oil while the right vial's mismatched tubes are exposed and visible.