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Spectrum Piano

The visible part of the electromagnetic spectrum is represented by less than an octave of the keys; UV, IR, and microwaves are also indicated.

What it shows:

The keys of a piano are used to represent the electromagnetic spectrum, illustrating the narrow range of frequencies that constitute the portion visible to human sight.

How it works:

An old piano 1 with its center octave of keys (C4=261.6Hz to C5=523.3Hz) colored for the visible spectrum (the seven colors spread to...

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Hear the Wall Bend

What it shows:  A room-size laser interferometer with audio signal output. A standing wave is produced whenever a wave is reflected back on itself. A resonant cavity requires a second reflection so that the twice reflected wave has the opportunity to be in phase with the original wave. Here, laser light is reflected from a half-silvered mirror (mounted on a wall) so as to return to the laser and be reflected again by the laser. Movement of the wall by half a wavelength is sufficient to change the cavity formed between laser mirror and wall mirror from one resonant...

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Rutherford Scattering

What it shows:

A qualitative demonstration of Rutherford's α-particle scattering experiment using magnetic pucks on an air table.

How it works:

In its simplest form, we use an Ealing air table, 1 1m square, with a fixed magnetic puck at the center. A second puck with the same polarity is repelled and scattered by the first; the scattering angle being dependant upon the impact parameter b (see figure 1). A more complex setup is described in the Comments.

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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...

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Reactionary Roadbed

Radio controlled car moves one way while road moves the other.

What it shows:

We tell our students that, when a car drives down the road, the road and the Earth move in the opposite direction, albeit imperceptibly. This demonstration is a realization of that concept, made possible (and perceptible) by the fact that the road is not attached to the Earth.

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Golf Ball Atmosphere

A model of molecular motion and pressure using practice golf balls.

What it shows:

The kinetic energy of gas molecules bouncing off a surface causes pressure.

Increasing the molecules' speeds increases the pressure and the volume of the gas.

 

How it works:

Plastic practice golf balls represent...

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Walk-In Faraday Cage

What it shows:

A lecturer's faith in the principle that an electric field cannot exist inside a charged conductor is put to the test using a Faraday cage that is large enough to sit in.

How it works:

The lecturer (or some volunteer) climbs the three steps and sits upon a plain wooden chair. Their assistant pulls the mesh door closed and fastens it. A Van de Graaff, whose dome is in contact with the cage, begins to charge itself and the cage up to a high voltage. The person inside is oblivious to the large amount of charge now...

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