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Tuning Forks

Selection of mounted tuning forks and rubber hammer.

How it works:

Each tuning fork is mounted on a wooden sound box to amplify the sound (they're very difficult to hear without the box). A microphone/preamp/scope setup may be used to visually demonstrate the pure sinusoidal sound wave. Additionally, a frequency analyzer shows a single frequency component (however, if the gain is turned up high, you may also see the frequency components due to the resonances of the sound box or harmonics of the tuning fork if it was whacked too hard). One of the...

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Energy Stored in a Capacitor

What it shows:

The electrical energy stored in a capacitor is converted to mechanical work, driving a motor and raising a weight.

How it works:

A motor 1 is mounted atop a 2.5m length of 2×4. As it turns, it raises a 1 lb mass on a string from the ground by wrapping the string around a spindle (figure 1). The motor is driven by the discharge of a 12800µF, 75V capacitor previously charged by a DC power supply. 2 A double throw switch allows a clean change-over from one circuit to the other.
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Hot Road Mirage

What it shows:

There are various types of mirages possible, the details depending on whether the hot air is above or below the cool air and how sharp the transition is from cool to warm. This demonstration simulates what happens when a dark asphalt road gets much hotter than the air around it--the air next to it becomes hotter than the higher air and light traveling through this temperature gradient is bent so much that it appears reflected. The shimmering water on a road's surface or the blue oasis in the desert are natural examples of blue skylight being...

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Electron Diffraction

What it shows:

Louis de Broglie predicted that matter under certain circumstances would exhibit wave-like properties. A proof of this is the repeat of X-ray diffraction experiments using electrons, whose de Broglie wavelengths at high accelerating potentials are similar to X-ray wavelengths. Here we accelerate electrons into crystal targets and get diffraction patterns identical to those from X-ray diffraction.

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BCC to FCC

The microcystaline structure of a steel wire changes from body-centered-cubic to face-centered-cubic as it is heated to red-hot.

What it shows:

Iron atoms are arranged in a body-centered cubic pattern (BCC) up to 1180 K. Above this temperature it makes a phase transition to a face-centered cubic lattice (FCC). The transition from BCC to FCC results in an 8 to 9% increase in density, causing the iron sample to shrink in size as it is heated above the transition temperature.

How it works:

A three meter length of iron...

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Armillary Sphere

Model to show celestial sphere; larger version has capacity to show lunar motions.

What it shows:

The position and motions of heavenly bodies are projected against a hypothetical sphere of infinite radius, centered on the Earth, called the Celestial Sphere. With this demo you can explain the motions of the stars and of the Sun, and show various aspects of the seasons.

How it works:

The main features of the sphere itself are shown schematically in figure 1. The spherical wire cage defines the celestial sphere, its...

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Thermocouple Brownie

A brownie pan with two food safe thermocouples, one in the brownie batter and one in the air next to the pan, is put in a pre-heated oven, and the temperature profiles recorded and displayed.

Clean copper wire is used to make an armature for the thermcouple wires. Crimp the center of a 20 cm piece of 14 ga wire on the side of the baking pan. Bend loops at the ends of the copper wire to hold the thermocouple wire.

The oven temperature thermocouple should be about five centimeters away from the pan, at the same level as the center of the pan. The brownie thermocouple is...

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