Aluminum Leslie's Cube, 10 cm Sides

Leslie's cube is a classic apparatus for demonstrating that the rate at which a surface radiates heat depends on its finish, not just its temperature. This version is a sealed aluminum box with 10 cm sides, built so that a single container at a uniform internal temperature presents four different external surfaces for direct comparison.

Each of the four vertical faces carries a different finish, one blackened, one roughened, one varnished, and one polished, while all four sit at the same temperature because they enclose the same body of heated water. This isolates surface emissivity as the only variable, so any difference a class measures between the faces can be attributed to finish alone. The matte black face approaches an ideal radiator and the polished metal face radiates the least, with the roughened and varnished faces falling between, giving students a clear ranking to record and explain.

The top opening is fitted with a stopper, and the cube is filled with water held near boiling by a low Bunsen flame beneath it, maintaining a steady internal temperature throughout the demonstration. An infrared sensor or thermopile aimed at each face in turn lets students compare the relative radiant heat output of the four surfaces and connect those readings to the concept of emissivity. The aluminum construction conducts heat efficiently from the water to the outer faces, keeping all four surfaces close to the same temperature for a fair comparison.