Mixing Light Colors with the Three Port Light Source


Marty SagendorfBy: Martin Sagendorf

We see hundreds of colors, but the colors we think we see are often not what we’re actually seeing – i.e. many of these colors are combinations of other colors.  ‘Light’s Story’ is fascinating and full of surprises.  It begins with knowing that radiating and re-radiating substances emit light.  The light colors emitted are functions of a number of factors: the substance, or the incident light, or the temperature of an incandescent source.

All the textbooks explain ‘additive’ and ‘subtractive’ colors.  Explanations are fine, but actual experience makes both an immediate impression and a very lasting learning experience.  For example, here’s how only RED, GREEN, and BLUE light colors combine to produce two new unexpected colors.

Mixing Light - Educational Innovations

But we’re getting ahead of ourselves… let’s start with something we’re really familiar with: pigment colors.  We all know that mixing different paint (pigment) colors will produce new colors.  For example, when we mix red and green pigments we ‘see’ brown. And, as everyone knows, mixing a wide range of pigment colors will produce the ‘color’ we see as black.  But, odd things happen when we mix two light colors.  We don’t get the same color that we obtained when we mixed pigments.

When we mix red and green light colors we don’t ‘see’ brown: we see yellow!  How can this be?  Then… even though it does appear even more counter-intuitive, the mixing of all light colors produces the color we ‘see’ as white (but has NO color? – white… or does it?). Read the rest of this entry »


Bring Some Magic Into Your Classroom!


Ted Beyer, Educational Innovationsby Ted Beyer

One of my favorite authors, Arthur C. Clark, once said, “Any sufficiently advanced technology is indistinguishable from magic.” This has been quoted, misquoted and reused for years.  Of course, it’s perfectly true, and magicians have been using science as part of their acts for centuries. Things that we take for granted today were once bleeding edge technology. I remember in high school reading that sometime ‘soon’ (this was more than 30 years ago) there would be TVs that would be so thin that they would hang on the wall like pictures – impossible! A generation before, the concept of television itself was astonishing, and a generation before that, moving pictures of any kind were magical.

As I started to think about this, I suddenly realized that there are many products that we sell here at Educational Innovations that are used – currently – by magicians as ‘tricks’ in their act. Let’s take a look…. Read the rest of this entry »


Concentrating Sunlight: It’s Easy!


Marty Sagendorfby: Martin Sagendorf

On a Bright Day:

A great deal of energy falls on the Earth’s surface – roughly 1 kW per square meter.  This is about 0.6 Watt per square inch.  This doesn’t sound like much energy, but suppose we collect and concentrate 63 square inches of this sunlight?  These 63 square inches would collect about 38 Watts of energy.  This doesn’t sound like much, but…

Suppose We Could Then:

Concentrate these 38 Watts into an area of only 1/8 of a square inch?  This is exactly what we can do with an inexpensive plastic Fresnel lens.  We’ll focus the sunlight into an area 3/8” in diameter – this is the equivalent of 300 Watts per square inch!  With this energy level, we can easily ignite a piece of wood, boil some water, and even melt a penny.

A Suitable Device:

Is described in the book, Physics Demonstration Apparatus and in the blog The Sun’s Energy.

Now we’re going to describe how to build a much simpler version that works just as well – one that uses a very inexpensive Fresnel lens and is very easy to construct. Read the rest of this entry »


Great Balls and Fire! Smashing Steel Spheres with Video


Tami O'Connor, Educational Innovationsby:  Tami O’Connor

When two 1-pound, 2-inch diameter, chrome steel spheres are smashed together, enough heat is generated at the point of contact to burn a hole in ordinary paper!  This dramatic demonstration has been a favorite of students in every grade for as long as I have been teaching!

Smashing Steel Sphere Demo KitThere are a few considerations when allowing students (especially younger ones) to conduct this activity on their own…  First, the spheres are pretty heavy, so if they were either dropped on a foot or onto a nice tile floor, the result would not be good.  Also, be sure that the only thing between the spheres is paper or aluminum foil.  Fingers caught between the colliding spheres would not  be happy.  Finally, all participants should wear safety glasses, as it is not unusual for a small piece of paper to fly off after the spheres collide.

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Chladni Plates


Marty Sagendorfby:  Martin Sagendorf

An Odd Name: They’re named for the German physicist Ernest Chladni who popularized them in the mid-1700s.  His name is pronounced: kläd’nêz.

Chladni Plates are: Thin plates (sprinkled with fine particles) vibrated perpendicular to their plane.

How? – Then and Now: Long ago Chladni used a cello bow to excite the edge of a thin metal or wooden plate.  Today, we can use an oscillator, amplifier, and an electro-mechanical oscillator.  We have a great advantage, we can easily vary the frequency of excitation thereby providing a whole vista of experimentation.

A 17 in. x 14 in. Chladni Plate in guitar shape at 200 Hz

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