Change of Volume with State

CO2 and He balloons in liquid nitrogen.

What it shows:

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.

How it works:...

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Greenhouse Bottles

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...

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Loaded Beam

loaded beamsBeam supported at ends with platform scales and toy truck as load to demonstrate moment arms.

What it shows:

The concept of moment arms is exemplified by this model of a truck on a bridge.

How it works:

A beam (board) supported...

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Pascal's Paradox

What it shows:

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). pascalSo how come the scales...

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TV Image Deflection

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.


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Edge Diffraction

What it shows:

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.


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Lead Bell

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...

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Metals in Acid

Curls of zinc and magnesium are dropped into 2M hydrochloric acid, and bubbles observer'd.

A 600ml beaker, clean and clear, is at the focal point of a camera projecting the image of 500 ml of 2M hydrochloric acid.

A curl of magnesium bubbles wildly, skittering across the surface of the acid.

A curl of zinc sinks to the bottom, and bubbles form at a steady rate.