Fiber Optics

What it shows:

Light is transmitted by a bundle of optical fibers and/or a coiled length of plastic rod, regardless of the twists and turns in the path it must negotiate. Total internal reflection keeps the light confined.

How it works:

A HeNe laser is used as the source of light. The bundle of optical fibers consists of a very large (but unknown) number of individual glass fibers measuring 0.05 mm (0.002") in diameter. About 30 cm of the bundle is exposed at the end while the rest of the length is protected by a rubber sheath....

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Fishtank TIR

What it shows:

A simple qualitative demonstration of total internal reflection using a laser beam.


How it works:

Using a fish tank suitably doped with a scattering agent (see Setting it Up), a ray of light from a laser beam can probe the water-air...

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Bouncing Light Beam

What it shows:

As a simulation of atmospheric refraction, this demonstration shows the gradual and continuous bending of light due to a gradient in the optical density of the medium. In this case the variable refracting medium is a tank of sugar water with a vertical gradient in the concentration of sugar and a HeNe laser provides the light beam. It can be used as a model of mirage formation (except that the direction of increasing refractive index is in the opposite direction) or even as a representation of the refraction of seismic waves through the Earth's...

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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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Hero's Shortest Path

What it shows:

Hero's Principle states that light undergoing a reflection from a plane surface will follow the path of least distance. Here is a mechanical analog showing that when the angle of incidence equals the angle of reflection, the path length is minimized.

How it works:

The light path is represented by a 2m length of nylon rope that runs from a fixed end, 'reflects' around a pulley, back up to a second pulley (figure 1). The surplus rope is held taught by a 1kg mass. The pulleys, 6cm in diameter are free to move...

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Electronic Pinhole Camera

What it shows:

The simplest method of controlling light to form an image is to use an opaque mask with a pinhole in it. Rectilinear propagation of light explains all (nearly). A video camera is substituted for the old prototypal shoe box so that an entire audience can see the pinhole image "live."

How it works:

An extremely light-sensitive video camera 1 sans lens substitutes for the pinhole camera box and film. The front of the Newvicon is the image plane and, as this sits right behind the faceplate of the camera...

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Optics Disk

What it shows:

All of the concepts summarized by the above keywords can be clearly and quantitatively demonstrated with this piece of apparatus.

How it works:

A light source 1 rotates around the circumference of a large white disk 2 with degree graduations around the entire perimeter. The collimated beam of light grazes the surface of the disk, creating a highly visible pencil of light, so that ray tracing is easily accomplished. A horizontal mirror, positioned at the center of the disk, is used for the law of...

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Infra-Red Projector

What it shows:

Like visible light, invisible infra-red radiation can be refracted by lenses to produce an image on a screen. Indeed, a slide projector designed for visible light is used as the imaging device; a heat- sensitive screen makes the invisible IR image visible.

How it works:

Our IR source is a 1000 watt "lantern slide" projector 1 from which we have removed the special heat-absorbing glass in the condenser assembly. The slide to be imaged is some kind of lettering, like the name of the course (Science A-29...

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Detection of IR radiation from hair dryer and/or special IR source.

What it Shows:

Detection of infra-red radiation by the rotation of a paddle-wheel vane inside a low pressure flask.

How it Works:

A radiometer consists of a partially evacuated flask containing a four bladed vane (see figure 1). One side of each blade is a matt black, the other silver. The black surface, being a better absorber and radiator of heat, warms the air above its surface more than the silver. The resulting higher kinetic energy of these air...

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Continuous Spectrum

What it shows:

White light is shown, á la Newton's demonstration of dispersion by a prism, to be composed of a continuous spectrum of colors.

How it works:

A large brilliant spectrum is produced by using a 1 kW carbon arc light source 1 with adjustable slit, a "fast" f/0.9 imaging lens, 2 and a highly dispersive in-line prism. 3 The spectrum easily fills a two meter wide screen with vibrant colors. An alternative (more compact) setup consists of a Beseler slide projector 4 which...

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Driven RLC Circuit

rlc circuit

What It Shows

The amplitudes and relative phases of the voltages across the individual elements of a series RLC circuit varies with the frequency of the driving voltage. The voltages of the three elements plus the driver are plotted simultaneously on an...

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Electromagnetic Spear

What it shows:

Static 3-D stylized model of an electromagnetic wave, with two sets of sinusoidal fins at 90° representing the E and B fields.

How it works:

The wave packet model consists of a wooden spine with E and B fins of 1cm wooden dowels. A plastic arrowhead gives the spine a direction.

Figure 1. The Spear


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