Presentations

Planck's Constant Determination

What it shows:

The photoemission of electrons from a metal surface depends on the energy of the incident radiation and not on its intensity. Knowing the energy of the emitted photoelectrons and the frequency of the incident light, you can calculate a value for Planck's constant h.

How it works:

Using a mercury source, we have at our disposal three very bright visible lines, in the blue, green and yellow (doublet), and a rich selection of ultra-violet. Our main source is a Phillips Lifeguard 1000W street lamp with its outer (uv...

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Roller Coaster Potential

What it shows:

Potential energy curve with potential barrier illustrates electron-atom, atom-atom or ion-ion interactions.

How it works:

This is a one dimensional potential well model with a potential hill that can be used to represent several scenarios. The wooden model is made of a sandwich of three strips of plywood (1/4"-1/2"-1/4") forming the cross section as shown in figure 1. A 1" ball bearing fits snugly enough into the groove that it won't fly out when it hits the barrier.

figure 1. The roller...

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Relativity Train

What it shows:

The Relativity Train is a realization of the famous Einstein gedanken experiments involving traveling trains carrying clocks and meter sticks. The demonstration is used to show how the preservation of the postulated constancy of physical laws and the speed of light in all inertial frames requires length contraction and time dilation in the train frame relative to the lab frame of reference. The demonstration is, of course, not a real experiment but rather a visual means of showing (without using any equations) how length contraction and time dilation are...

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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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Crystal Growth & Recession

What it shows:

By providing a cold boundary, you can get water to crystalize as advancing needles of ice.

How it works:

This cold boundary can be provided by a petri dish of alcohol. Adding dry ice to this produces an endothermic reaction that lowers the temperature below 0°C. By placing a smaller petri dish containing distilled water within the alcohol dish (figure 1), the water freezes from the outer edge inwards. In front of a "thick" wall of ice shoots a monolayer of needles. The advance or recession can be...

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Centrifugal Eggbeater

Spinning frame that demonstrates equatorial bulge (oblateness).

What it shows:

The rotation of a planet about its axis causes its equator to bulge due to the "centrifugal force" acting on its mass. Here a spinning wire frame simulates the effect.

How it works:

Planets are actually oblate spheroids rather than spheres due to their rotation. This device consists of two spring metal rings mounted on a metal axis. The north pole is free to slide so that, as the frame spins, the hoops flatten and the equator bulges. The axis is...

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Conductivity of Solutions

A light bulb is lit when the conductivity probe is immersed in an ionic solution.

The solutions are all in labeled 250ml beakers. All are about 150 ml of 0.1M sol'n. In order, the solutions are: tap water, distilled water, sodium chloride, sucrose, acetic acid, hydrochloric acid, sodium hydroxide, ethanol, and barium sulfate. (See video: http://youtu.be/4WillWjxRWw?hd=1)

The simple conductivity tester is on the bench, for the instructor to plug in. An 800ml beaker with 400 ml of distilled water is provided as...

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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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Telescope Resolution

What it shows

A telescope (with video output) at the front of the lecture hall is focused on two point light sources at the rear of the hall. Although the light sources are only 1/2 mm apart, they are readily resolved. The Rayleigh limit of resolution can be clearly shown by reducing the telescope aperture to the point where the two light sources can barely be resolved, similar to the following images (from: Cagnet/Francon/Thrierr, Atlas of Optical Phenomena). At the Rayleigh limit the centers of both point sources coincide with the the first minimum of the other source....

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Friction

The topic of friction can be a little dry. Consider lubricating students' interest with these two examples

Friction around Pole

What it shows:  Many people have probably observed that, by wrapping a rope around a post, a person can hold in check a much larger force than would ordinarily be possible. In this experiment a flexible thick rope is wound around a horizontal pipe. Due to the interaction of the frictional forces and tension, there can be a considerable difference in tension between the two ends of the rope. In the demonstration, one end of the...

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