[★★★]

Chaotic Pendulum

Coupled, double, physical pendulum executes chaotic motion when non-linear initial conditions are imposed.

What it shows:

A double pendulum executes simple harmonic motion (two normal modes) when displacements from equilibrium are small. However, when large displacements are imposed, the non-linear system becomes dramatically chaotic in its motion and demonstrates that deterministic systems are not necessarily predictable.

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Beats

Two tuning forks with similar frequencies; one fork is variable in frequency to tune beating.

What it shows:

The interference of waves from two tuning forks of slightly differing frequencies gives rise to beating, that is, a modulated wave of frequency.

νb = (ν1 - ν2)

How it works:

Using two tuning forks of 256Hz, with one of the pair having small clamps (see figure 1) attached to the fork's limbs. These alter the fork's resonant frequency, and adjustment of the clamp...

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Eddy Current Damping

What it shows:

A sheet of aluminum falls slowly between the poles of a magnet because induced currents in the sheet set up magnetic fields which oppose the motion.

How it works:

As the aluminum sheet falls between the poles of the magnet, eddy currents are induced in the metal. These currents set up their own magnetic fields, which through Lenz's law oppose the change that caused them. As the cause is gravity pulling the sheet to Earth, the sheet decelerates as it passes between the poles of the magnet, only to accelerate again...

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Optics Disk

What it shows:

All of the concepts summarized by the above keywords can be clearly and quantitatively demonstrated with this piece of apparatus.

How it works:

A light source 1 rotates around the circumference of a large white disk 2 with degree graduations around the entire perimeter. The collimated beam of light grazes the surface of the disk, creating a highly visible pencil of light, so that ray tracing is easily accomplished. A horizontal mirror, positioned at the center of the disk, is used for the law of...

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Photoelectric Effect

What it shows:

A direct observation that the photoelectric effect is color (i.e. frequency) dependent and not intensity dependent. We discharge an electroscope using UV radiation after all attempts to discharge it with light of a longer wavelength has failed.

How it works:

An ebonite rod and fur is used to place a negative charge onto a Braun electroscope (figure 1) fitted with a thick zinc plate. Deviation of the electroscope arm from the vertical indicates a net negative charge. Next we hit it with light from a 1000W...

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Faraday Induction

What it shows:

The mathematical description of electromagnetic induction as formulated by Maxwell and Faraday requires two different sets of equations to calculate the induced voltage, depending on whether the coil is stationary and the magnet moving or vice versa. In fact, as this demonstration shows, the voltage is the same as predicted by the two sets of equations.

How it works:

The apparatus is identical to demonstration Faraday's Law, and is described in detail there. Briefly, it consists of a galvanometer hooked up to a...

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Superconductivity

What it shows:

A superconducting material in the presence of a magnetic field excludes that field from its interior. This is shown by levitating a magnet above a high temperature superconductor.

How it works:

We have a 25mm disc of ceramic yttrium barium copper oxide YBa2Cu3O7 that becomes superconducting above liquid nitrogen temperatures (Tc = 90K). Using a cubic neodymium magnet 4mm of side, two effects can be shown. Firstly, the Meissner effect itself, by placing the magnet on the...

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Reaction of Propane and Oxygen

An oxy-propane torch is lit with just propane, and the flame examined, before oxygen is added, changing the flame character and temperature.

The torch head is gaffed to the table top with enough slack to turn the gas valves. The propane tank and the oxygen tank are on separate dollies. The torch valves are closed, and the tank regulators set so there is about three pounds of pressure behind each gas. (The precise settings of the regulator are a good thing to check out in a practice session before doing this demo.)

With a friction lighter in one hand, open the propane valve on...

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