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Conservation of Charge to 3 Sig Figs

What it shows:

Electricity is never created or destroyed, but only transferred. Rubbing fur and Teflon™ together transfers charge (electrons) from the fur to the Teflon, making the Teflon negatively charged. Conservation of charge requires the fur to become equally and oppositely charged as is demonstrated in this experiment to an accuracy of ≤1%.

How it works:

The difficulty in demonstrating charge conservation quantitatively lies in catching all the charge before it leaks away, the fur being the main problem. This is overcome...

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Back EMF

What it shows:

A sudden change in current in an inductor - resistor circuit produces a very large back EMF. If that resistance is a bulb, it will shine much brighter during the change than during DC flow.

E = -LdI/dt

How it works:

The circuit consists of a 6V bulb connected in parallel with a 10.5mH inductor coil as in figure 1. With the battery connected, the bulb burns at its rated 6V. Disconnecting the battery sends the applied voltage and hence the current to zero. The rapidly collapsing...

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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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Polarization by Absorption

What it shows:

Polaroid filters absorb one component of polarization while transmitting the perpendicular components. The intensity of transmitted light depends on the relative orientation between the polarization direction of the incoming light and the polarization axis of the filter.

...

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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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Thermal Expansion

Brass ball doesn't fit through brass ring until ring is heated.

What it shows:

Most solids (see Comments) expand when heated due to increased atomic and lattice vibrations. In this demo, a brass ring expands when heated to let a previously too small a ball pass cleanly through.

How it works:

The apparatus consists of a brass ring on a handle (figure 1), attached by a chain to a brass ball. Demonstrate that the ball is too large to pass through the ring, then heat the ring over a blue Bunsen flame for about a minute. The...

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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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Smog in a Bottle

Nitrogen dioxide is produced by an electric discharge in air and, when sprayed with a water mist, produces acid rain.

What it shows:

Some of the most irritating and dangerous pollutants in our atmosphere are gases such as sulfur dioxide and nitrogen dioxide. Nitrogen dioxide is a deep orange-red gas that, together with smokelike particles, is responsible for the color of smog. In this demonstration, nitrogen dioxide is produced by an electric discharge in air and, when sprayed with a water mist, produces acid rain.

How it works:...

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Bernoulli Beach Ball

What it shows

Bernoulli's principle shows the velocity dependence of pressure in a fluid. Here, fast flowing air creates a zone of low pressure that holds a beach ball aloft.

beach ball held aloft by fast flowing air from a blower

How it works

Here we have a beach ball held in the air stream from a...

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Length Measurement

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Standard meter sticks and selection of cubic volumes. 

What It Shows

No temperature-controlled platinum rods here – just some sticks that are very close to a meter in length. Standard meter sticks as well as cubic centimeters and decimeters are available for reference and/or comparison. Other volumes include a 22.4 liter cube (to get the sense of the size of a mole of gas). Sets of calibrated weights include both metric and English standards from milligrams to several kilograms. Various types of analytical balances and scales are also available:...

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