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...
Three containers are filled with water to the same depth, and each has the same base surface area (see figure 1). Since the pressure and area are the same in each container, the force should be the same (pressure = force/area). So how come the scales...
Image on black and white television is deflected by a magnet, not unlike the Maltese Cross.
What it shows: The television is basically a sophisticated cathode ray tube. The electron beam in the TV is influenced by magnetic fields in the same way as in Crookes tubes.
How it works: The image on a black & white TV is formed by a single electron gun scanning the screen. Holding a strong magnet to the side or in front of the screen deflects the beam from its regular sweep pattern, distorting the image.
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.
Dull at room temperature, rings clearly after immersion in liquid nitrogen.
What it shows:
A lead bell, dull sounding at room temperature, rings brightly when cooled to liquid nitrogen temperatures.
How it works:
A lead bell at room temperature is dull in more ways than one. But its elasticity is temperature dependant, with an increase in elasticity as its temperature decreases. This increase in elastic modulus narrows the resonance response with frequency and increases the quality Q of the lead as...
Allow a board to rotate under the force of gravity and the free end will accelerate at a rate greater than g. Relation between angular acceleration and linear acceleration seems to give free-fall paradox.