Wien's Displacement Law

Changes in the spectral intensity distribution of a hot tungsten filament are observed as the temperature is varied.


How It Works

A slide projector (Beseler Slide King II) with a 1kW lamp and adjustable lens is plugged into a Variac. The light from the projector passes through an inline...

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Brewster's Angle

What it shows:

When unpolarized light is reflected from a non-metallic surface, the reflected ray is plane polarized parallel to the reflecting surface if

θi + θr = 90°


tanθi = n

where θi = incident ray (Brewster's angle), θr = refracted ray, n = refractive index

How it works:

We use a black vinyl sheet 1m×4m as the reflecting surface, which has a Brewster angle of 57°. A theatrical spot lamp 1 is used to give a 50cm circle...

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Rayleigh's Criterion

What it shows:

The criterion for the resolution of two sources is that the central maximum of the single slit interference pattern of one source falls on the first minimum of the pattern of the second source.

How it works:

Each laser beam passing through the slit will form a diffraction pattern on the screen. With the aperture closed down, the pattern will be spread out and the central maxima of both sources will overlap giving a blurry image. Opening up the aperture and the diffraction patterns will get narrower, until the point...

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Poisson's Spot

Diffraction produces a bright spot where Poisson believed there would be darkness.

Poisson's Spot

What It Shows

Edge diffraction around a 1/8" diameter steel ball bearing results in a visible spot in the center of its shadow. In 1818 this result—to the chagrin of Siméon D. Poisson—...

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Single Photon Interference

Wave/particle duality observed in Young's double slit experiment with camera sensitive to individual photons.

What it shows:
In this demonstration we perform the double-slit interference experiment with extremely dim light and show that even when the light intensity is reduced down to several photons/sec, the audience can see the familiar Young's double-slit interference pattern build up over a period of time. This addresses the question of how can single photons interfere with photons that have already gone through the apparatus in the past, or with those that...

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Edge Diffraction

What it shows:

A point light source will produce seemingly sharp shadows which turn out to be not at all sharp when viewed under magnification. Narrow interference bands are seen within the shadow of a straight edge while more complicated shapes yield more complicated interference bands and striations.


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Hear the Wall Bend

What it shows:  A room-size laser interferometer with audio signal output. A standing wave is produced whenever a wave is reflected back on itself. A resonant cavity requires a second reflection so that the twice reflected wave has the opportunity to be in phase with the original wave. Here, laser light is reflected from a half-silvered mirror (mounted on a wall) so as to return to the laser and be reflected again by the laser. Movement of the wall by half a wavelength is sufficient to change the cavity formed between laser mirror and wall mirror from one resonant...

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Schlieren Optics

Optical technique that allows us to see small changes in the refractivity of air and other transparent media.

What it Shows

Refraction due to inhomogeneity in air is made visible by our single-mirror schlieren optics setup. The refraction can be caused by changes in the density, temperature, or pressure of the air immediately...

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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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Hotplate Mirage

What it shows:

A beam of light is distorted due to turbulent convection currents in air. This is a model of atmospheric distortion that affects seeing conditions in ground based optical and infrared astronomy.

How it works:

Turbulent air is provided by an electric stove ring, that heats the air above it as the warm earth dues to air sitting above it. The turbulent currents set up alter the refractive index of the air in a disordered and rapidly changing way. Light from a point source passing through these conditions is blurred...

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Florence's Rainbow

What it shows:

A beam of white light incident on a giant raindrop (simulated by a water-filled round flask) produces a full rainbow of colors. As with real rainbows, one can also see that the light intensity inside the rainbow is much greater than outside the rainbow.

How it works:

A Florence (round-bottomed) flask is completely filled with water and sealed with a rubber stopper. A Beseler slide projector 1 serves as the sunlight. The light incident on the giant raindrop is refracted, reflected, and refracted once more, back in the direction of the...

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Wheel & Axle Wavefront

wheel & axelWhat it shows:
A mechanical analogy of a wave front consisting of two wheels linked by an axle. It simulates refraction by rolling across a boundary between two surfaces having different rolling friction and thus altered propagation velocities.


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