Liquid Crystal Sheets

What it shows:

The selective reflection of a specific wavelength of light through a chiral nematic liquid crystal is temperature dependent and forms the basis for LCD thermograms and thermometers.

How it works:

Liquid crystals are an intermediate state of matter or mesophase between (crystalline) solid and liquid. Substances that have a mesophase have a non-flexible rod-like molecular structure. Although in a liquid phase, the shape of the molecule and intermolecular forces means that the molecules retain a common preferred...

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Iron Tin Reaction Kinetics

Dark red iron[III] solution is rapidly reduced to colorless iron[II] by addition of tin[II] chloride solution, with the rate depending on concentration and temperature.

Four medium footed cylinders are prepared with 100 ml of ferric chloride solution 0.01M with potassium thiocyanate solution added to make the dark red complex. One of the solutions should be hot, so just the iron and thiocyanate solutions in that cylinder, with a 150ml beaker for the demonstrator to fill with hot water from the water cooler, right before the demonstration.

The cylinders are on the bench top in...

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Capacitance of Human Body

What it shows:

Determine the capacitance of the human body as follows. Charge a person of unkown capacitance to 1000 volts. The person is subsequently connected (in parallel) to an external capacitor of known capacitance. The voltage measured across the capacitor combination allows one to determine the unknown capacitance of the person (typically between 180 — 200 pF).

How it works:

A 1000 volt power supply (output is in the microamp range) is used to put charge on a person. We assume that the amount of charge transferred to the...

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Double Refraction

What it shows:

A birefringent substance will split unpolarized light into two polarized rays with different refractive indices and different velocities. A crystal of calcite demonstrates this phenomenon.

Double Refraction...

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Supersaturation and Crystallization

What it shows:

A supersaturated solution is unstable, and by seeding it you can trigger rapid crystallization.

How it works:

Sodium acetate can dissolve in water in great quantities at high temperature, and if you let the solution cool carefully to around room temperature, you have a clear supersaturated solution. Disturbing this unstable equilibrium by dropping a small crystal of sodium acetate into the solution makes the whole thing solidify; the sodium acetate crystals growing radially outwards from the impact point of the...

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Vacuum Infusion

A vacuum is drawn over a beaker of sliced cucumber covered in a clear dressing. The cucumber outgases, making bubbles. When the atmosphere is readmitted, the dressing is forced into the cucumber, rendering it translucent and seasoned. 

A polycarbonate bell jar with a volume of about three liters is centered on the base, with attention to the seal. The vacuum pump tube ID is the same as the outlet tube OD, so attach by hand. Vacuum release by sliding the vinyl tube off of the outlet. 

The vacuum pump is the oil-less variety, and is not bothered by water. The pump is...

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Hand Battery

Copper and zinc plates connected by micro-ammeter; your hand completes the circuit.

Clean copper and zinc sheet metal stock is cut into strips or pads. Alligator clip a zinc strip and a copper strip and plug the leads into a modern multimeter. DC 2V scale should cover the 1.09V that we expect from a zinc/copper battery at standard conditions of 1 Molar electrolyte and room temperature.

Our fingers are a network of electrolytic conductors, with more or less conductance (depending on moisture and salt). Pressed to the metal strips, adjacent fingers complete the circuit and...

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