Critical Opalescence

What it shows:

The demonstration shows density fluctuations in liquids. These fluctuations are particularly spectacular near critical points. A binary fluid mixture of methanol (29% by weight) and cyclohexane (71%) becomes opalescent when heated up to its critical temperature (about 45˚C) ... the fluids become miscible above this temperature.

How it works:

The two fluids are sealed in a special vial, able to withstand elevated pressure. The fluids are immiscible at room temperature. When brought up to 45˚C, they become miscible...

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Precipitation of Lead Iodide

Potassium iodide solution is added to lead nitrate solution, and bright yellow lead iodide precipitates.

Potassium iodide solution is 0.1 M and lead nitrate solution is 0.01M.

The lead nitrate solution is about 350 ml in a 600ml beaker, and the KI sol'n is 200 ml in a 400ml beaker. Pour the potassium iodide sol'n into the lead nitrate.

Glasses and gloves. The finished demonstration is stirred and the precipitate and solution goes in the hazardous waste bucket.

Incompressibility of Water

What it shows

The bulk modulus of water is about 2.2 x 109 Pa, which means that a change of 1 N/m2 of external pressure on the liquid is able to change a given volume of it by a factor of 4.5 x 10-10 (for comparison, the same pressure change would produce a volume change of about 7 x 10-6 for air and 7 x 10-12 for cast steel ). So if we can completely fill a Florence flask with water, we can use it as a hammer to drive a nail into a board!


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Inverted Pendulum

A physical pendulum finds stability in its inverted position when driven at the proper frequency and amplitude combination.

How it works

The physical pendulum is a 45 cm x 2 cm x 6 mm (1/4") strip mounted on a ball-bearing pivot and can rotate 360 degrees. Its pivot is driven by a 3/4" stroke Sears Craftsman Auto Scroller Saw (...

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OHP RLC Circuit

What It Shows

The current in a circuit consisting of a capacitor, inductor, and resistor will oscillate back and forth as the capacitor charges and discharges.

How It Works

The circuit layout is shown in the figure below. Initially the knife switch links the capacitor to the battery. Switching to complete the LRC circuit allows the capacitor to discharge. The current I in the circuit increases, as does the magneic field B inside the inductor. When the capacitor charge is zero, I and B are a maximum (the energy of the circuit is now stored in the inductor). As the...

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Metals in Acid

Curls of zinc and magnesium are dropped into 2M hydrochloric acid, and bubbles observer'd.

A 600ml beaker, clean and clear, is at the focal point of a camera projecting the image of 500 ml of 2M hydrochloric acid.

A curl of magnesium bubbles wildly, skittering across the surface of the acid.

A curl of zinc sinks to the bottom, and bubbles form at a steady rate.