Presentations

Simple Harmonic Motion Demonstrator

Relation between circular motion and linear displacement on overhead projector.

What It Shows

Uniform circular motion can be shown to be the superposition of simple harmonic motions in two mutually perpendicular directions. This apparatus gives the audience a visual display of how one dimensional simple harmonic motion varies in unison with circular motion.

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Conductivity of Glass

Insulating glass becomes a conductor of electricity when heated red-hot with a blowtorch. (m) (T+)

What it Shows

At room temerature, glass is almost as good an insulator as hard rubber. When heated to 1000 K, however, glass has a resistivity of less than 107 ohm-meters (Purcell1 fig. 4.8 pp 140). As glass becomes molten the once immobile ions are able to drift further between collisions under the influence of an applied electric field (Purcell pp 139). We can dramatically observe this decreased resistance using a blowtorch and a few incandescent… Read more about Conductivity of Glass

The Barkhausen Effect

What it shows:

The magnetization of a ferromagnetic substance occurs in little jumps as the magnetic moments of small bunches of atoms, called domains, align themselves with the external field. We can actually "hear" the switching of these domains by amplifying the currents induced in a coil that surround the ferromagnetic material.

How it works:

We use two 10mH coils mounted back-to-back to cut out AC noise. The samples, listed in Fig.1 are in wire form, about 3-5cm in length and pushed through corks so they can sit… Read more about The Barkhausen Effect

Hotplate Mirage

What it shows:

A beam of light is distorted due to turbulent convection currents in air. This is a model of atmospheric distortion that affects seeing conditions in ground based optical and infrared astronomy.

How it works:

Turbulent air is provided by an electric stove ring, that heats the air above it as the warm earth dues to air sitting above it. The turbulent currents set up alter the refractive index of the air in a disordered and rapidly changing way. Light from a point source passing through these conditions is blurred… Read more about Hotplate Mirage

Tether-ball Catastrophe

What it shows:

An accelerated electric charge radiates energy. So according to classical physics, an electron in orbit about an atomic nucleus should emit electromagnetic radiation by virtue of its orbital motion. As it radiates energy, the radius of its orbit decreases. The electron should spiral into the nucleus amidst a burst of radiation in about 10-16 seconds.

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Uranium Block

What it shows:

This block of uranium is of great historical significance -- it is a remnant of the WWII German Atomic Bomb Project. It was brought to Harvard by Prof. Edwin C. Kemble, Physics Dept. Chairman and also Deputy Science Director of the ALSOS mission in 1945. The American ALSOS mission was an intelligence effort to discover the extent of German progress toward atomic weapon development and its ultimate purpose was to secure all the uranium ore the Germans had confiscated during the war and finally close the books on the German program to build an atom… Read more about Uranium Block

Copper and Bulb

Copper has positive temperature coefficient; light bulb gets brighter when copper leads are dipped in liquid N2.

What it shows: 

Copper has a positive temperature coefficient (≈ 3.9×10-3 per ˚C), which means that its resistance drops with temperature. Here copper wire is immersed in liquid nitrogen (77˚K = -196˚C), decreasing its resistance (from room temperature) by almost a factor of 2, thus increasing the current flow though a circuit.

How it works: 

We have a coil of 30AWG copper wire wrapped around… Read more about Copper and Bulb

Precipitation of Silver Chloride

Sodium chloride solution is added to silver nitrate solution and a white precipitate of silver chloride is instantly formed.

The silver nitrate solution is around 0.1M, and the sodium chloride solution around 0.5M. Pour the sodium chloride sol'n into the silver nitrate to avoid leaving traces of silver nitrate in the empty beaker.

Wear safety glasses and gloves to prepare and perform this demonstration.

Ptolemaic Epicycle Machine

What it shows:  Long before the time of Copernicus, the Greek astronomer Claudius Ptolemy created a model of all the planets' observed celestial motions. The model involved combinations of perfect circles rotating with uniform speed. Ptolemy explained the apparent "looping motion" of the planets by placing the center of one rotating circle, called the epicycle, which carried the planet, on another rotating circle, called the deferent, so that together the motions of the two circles produced the observed looping motion of the planet. Moreover, the model… Read more about Ptolemaic Epicycle Machine

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