What it shows: A mechanical analogy of a wave front consisting of two wheels linked by an axle. It simulates refraction by rolling across a boundary between two surfaces having different rolling friction and thus altered propagation velocities.
A point light source will produce seemingly sharp shadows which turn out to be not at all sharp when viewed under magnification. Narrow interference bands are seen within the shadow of a straight edge while more complicated shapes yield more complicated interference bands and striations.
Cooling a gas causes a proportional decrease in volume with the drop in absolute temperature. A gas such as helium, which remains close to ideal at low temperatures, shows a four-fold decrease in volume when taken from room temperature 330K to liquid nitrogen temperature, 77K. Carbon dioxide however, sublimes at 194.5K, so is solid at 77K. Oxygen liquefies at 90K (S.T.P.). A qualitative demonstration of these effects can be shown with gas filled balloons.
Simulation of the greenhouse effect with silvered and unsilvered glass bottles.
What it shows:
Heat energy readily escapes from a clear glass flask, but is trapped inside a silvered flask which rapidly heats up.
How it works:
Two 2L flat bottom Florence flasks, one clear and one silvered (see reference), have identical 10Ω, 25W resistors placed inside them connected in series to a DC supply 1 These resistors act as good sources of infrared radiation. The clear flask readily transmits the IR, but the silvered...
An oxy-propane torch is lit with just propane, and the flame examined, before oxygen is added, changing the flame character and temperature.
The torch head is gaffed to the table top with enough slack to turn the gas valves. The propane tank and the oxygen tank are on separate dollies. The torch valves are closed, and the tank regulators set so there is about three pounds of pressure behind each gas. (The precise settings of the regulator are a good thing to check out in a practice session before doing this demo.)
With a friction lighter in one hand, open the propane valve on...