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Seismic Wave Refraction

Total internal refraction of laser beam through sugar solution with refractive index gradient; representative of seismic waves through Earth's mantle.

What it shows:

As a simulation of atmospheric refraction, this demonstration shows the gradual and continuous bending of light due to a gradient in the optical density of the medium. In this case the variable refracting medium is a tank of sugar water with a vertical gradient in the concentration of sugar and a HeNe laser provides the light beam. It can be used as a model of mirage formation (except that the...

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Egg Shell Strength

What it shows:

Eggs have a reputation for being quite strong under compressional loads. You won't believe your eyes when you see how strong they actually are — an egg can support a person!

How it works:

An egg shell is a composite material, but primarily calcium carbonate, "nature's ceramic."1 We assume the ultimate compressional strength of the material to be about the same as bone (which is mostly calcium phosphate, but never mind): 170x106 N/m2. The diameter of a "large" chicken egg is about 1.75" and the typical shell...

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γ Ray Inverse Square Law

What it shows:

Gamma rays are electromagnetic radiations which we detect as quanta of energy or photons. When the radioactive source is confined so that it acts as a point source, the diminution in the number of photons incident on a given area is such that the intensity is inversely proportional to the square of its distance from the source.

How it works:

A Co-60 source (1.173 and 1.332 MeV gammas) radiates isotropically. A Geiger-Müller counter is used to detect the radiation intensity at distances of 2, 3, and 4 meters. The...

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Samples of Elements

First day of Gen Chem: Metals and non-metals; solids, liquid and gas elements; compound of elements.

Copper, sulfur, lead, iron, antimony, iodine, carbon as powder and graphite sample, mercury, copper iodate, oxygen balloon.

Inverted Pascal Experiment

What it shows:

This is a concept question relating to Pascal's cask-bursting experiment. Imagine the experiment inverted—literally! Attach a 20-ft length of tubing to the opening of a can full of water. Turn the can upside down and raise it high. Will the water stay in the can, or will it run out? Will atmospheric pressure hold up the column of water in the tubing? What will happen? Have the class vote.

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TV Color Perception

What it shows:

The full spectrum of colors (including white) in a television picture is produced by the additive mixing of only three colors: red, green, and blue.

How it works:

In a color television tube, three separate electron beams are focused so as to strike the appropriate phosphor dot on the screen. By looking at the television screen under considerable magnification, one can clearly see that there are only three phosphors which are stimulated by the electron beam(s). The apparatus is diagrammed below.

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β-Ray Deflection

What it shows:

β-rays emanating from a radioactive isotope are deflected from their straight line paths by a magnetic field.

beta particle

How it works:

90Sr/90Y, a "pure" beta-minus source, emits a continuous spectrum of...

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