Thermal Physics

Copper and Bulb

Copper has positive temperature coefficient; light bulb gets brighter when copper leads are dipped in liquid N2.

What it shows: 

Copper has a positive temperature coefficient (≈ 3.9×10-3 per ˚C), which means that its resistance drops with temperature. Here copper wire is immersed in liquid nitrogen (77˚K = -196˚C), decreasing its resistance (from room temperature) by almost a factor of 2, thus increasing the current flow though a circuit.

How it works: 

We have a coil of 30AWG copper wire...

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Jumping Ring

Shoot the ring through the roof after dipping it in liquid N2; Lenz's law induced EMF in metal ring.

What it shows: 

The induced current in a metal ring is dramatically increased by lowering the ring's temperature.

How it works: 

Here is an extension of the ...

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Meissner Effect

What it shows:

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

...

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Lead Bell

Dull at room temperature, rings clearly after immersion in liquid nitrogen.

What it shows: 

A lead bell, dull sounding at room temperature, rings brightly when cooled to liquid nitrogen temperatures.

How it works: 

A lead bell at room temperature is dull in more ways than one. But its elasticity is temperature dependant, with an increase in elasticity as its temperature decreases. This increase in elastic modulus narrows the resonance response with frequency and increases the quality Q of the lead as...

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Everyday objects at low temperature

What it shows:

Mechanical properties of some materials change dramatically with temperature. These changes have entertaining effects on everyday objects by taking them from room temperature 300K to the temperature of liquid nitrogen 77K.

How it works:

Place your everyday objects in a dewar of liquid nitrogen for several minutes (at least until the LN2 stops boiling). Some examples to use:

1. Rubber gloves freeze solid and shatter on impact with floor.
2. Use a banana to hammer a nail into wood
3. Frozen...

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Collapse of 55 Gallon Drum

Drum evacuated by vacuum pump; crushed by atmospheric bombardment.

What it shows:

With an air pressure of 105 Nm-2 at sea level, even a heavy duty oil drum will be crushed if it has nothing inside to balance the pressure.

How it works:

The screw cap on the drum is fitted with a vacuum pump connector. Simply turn on the pump and wait; it takes about 8 minutes to pump down, so you can carry on with what you were doing interrupted by various creaks and bangs as the drum's side walls begin to give....

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Brownian Motion of Smoke Particles

Smoke cell under microscope; smoke particles seen bombarded by air molecules.

What it shows:

Brownian motion shows direct evidence of the incessant motion of matter due to thermal energy. Here we use the random bombardment of smoke particles by air molecules.

How it works:

The CENCO Brownian Movement Apparatus consists of a metal chamber with a glass viewing window on top and a lens on one side (see figure 1). Smoke from a piece of smoldering rope or match is drawn into the chamber through an inlet tube by...

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OHP Kinetic Theory Model

Simulation of molecular motion (Brownian, diffusion, etc.) with ball bearings on shaking table.

What it shows:

Two dimensional simulations of molecular dynamics and crystal structure using ball bearings. It can be used to show qualitatively the dynamics of liquids and gases, and illustrate crystalline forms and dislocations.

How it works:

The molecular dynamics simulator is more commonly known as a shaking table. It consists primarily of a circular shallow walled glass table that is oscillated vertically so as to vibrate and...

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Mixing and Unmixing

Food coloring in glycerine is mixed by turning a drum, then unmixed by reversing. Has entropy decreased?

What it shows:

Ink is squirted into a fluid and mixed in until it disappears. By precisely undoing the motions in the reverse direction, the ink becomes unmixed! The demonstration seems to defy thermodynamics in that it appears that entropy decreases, but in actuality the reversible mixing is made possible by insuring that the mixing/unmixing is done without turbulence.

How it works:

The space between two, transparent and concentric...

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Adiabatic Heating

Compression of gas within bicycle pump heats gas; alternatively, syringe PV=nRT (w/ Mac TC read-out).

What it shows:

An adiabatic process is one where no heat enters or leaves a system. Here we compress a gas adiabatically inside a bicycle pump. The work done on the gas increases its internal energy, so increasing its temperature in accordance with the first law of thermodynamics.

Increase in internal energy dU = dW the work done on the system

How it works:

Instead of allowing the air out of a bicycle pump we've...

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Bag of Lead Shot

Dropping bag containing lead turns gravitational potential energy to heat.

What it shows: 

A demonstration of the conversion of gravitational potential energy to heat energy. A bag of lead shot, repeatedly dropped to the ground, will heat up.

How it works: 

Lead has a sufficiently low specific heat capacity (128 J/kg/K) that a 5kg bag dropped five times from a height of 1.0m onto a rigid floor should increase in temperature by about 2K. The shot is contained in a bank deposit bag with reinforced...

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Convection Cell (Thymol Blue Cell)

What it shows:

Here we set up a convection cycle, where we heat part of a fluid; it expands, rises, then cools and sinks. A two dimensional model for real convection cycles in the atmosphere, oceans or stellar interiors.

How it works:

The convection cell is made from two sheets of 0.5cm plexiglass (front clear, rear translucent), separated by a 0.5cm gap for the liquid, the indicator thymol blue. The sides are plexi and the top left open, but the bottom is sealed with a hollowed brass rod. The brass serves two purposes. Firstly...

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Convection Cell

What it shows:

Hot fluid rises, cool fluid sinks. Here is a desktop convection cell modeling the processes in the atmosphere, oceans or stellar interiors.

How it works:

The currents are set up in rheoscopic fluid 1 (basically minute aluminum flakes in water) in a small 10×10×15cm glass tank. Half the base of the tank rests on a heater, the other on an aluminum block that acts as a heat sink. The rheoscopic fluid has a weird metallic sheen such that the bulk motion of fluid is clearly seen from the changing reflectivity....

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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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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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