April 19, 2010
by: Bennett M. Harris
It never fails. I get the same reaction, whether I present to seasoned physicists, grade level science teachers or even from the most discerning audience I’ve had; a group of fifty – fourth grade students, jaws gape and sounds of oohs, aahs and wows issue forth.
I’ve been in rooms surrounded by hundreds of artificial light sources, from the simplest incandescent bulbs to the most advanced OLED displays, and even so, when a person closes that knife switch and current begins to flow and a simple piece of pencil lead held suspended inside a partially evacuated chamber starts to glow brighter, brighter, and finally white light illuminates the chamber, something happens in the person’s brain. At once they are connected with the wonders that Sir Humphry Davy, Swan, and Edison felt when they experimented with the world’s first electrical light sources. Questions start to form; How does that work? How could we make it last longer? What would happen if we changed the carbon for some other material? All at once, the passive viewer is thinking scientifically, asking questions, and yearning to do more.
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April 6, 2010
by: Martin Sagendorf
Taking a photo in the UV is relatively easy and produces a somewhat different view of what we see in visible light. All that’s required is a small bi-convex lens, a cardboard box, some pieces of thin cardboard, a pack of ‘Sun Paper’, and patience.
As we know, sunlight contains ultraviolet, visible, and infrared ‘colors’, and we can ‘see’ only the middle wavelengths of this ‘optical spectrum’. Infrared is invisible, but we feel it as heat and likewise, at the other end of the spectrum (at much shorter wavelengths), the ultraviolet radiation is also invisible, but it is very energetic and damaging (as shown by the fading of paint and our sunburned skin).
So the question is, “How can we see UV?” Well, we can’t do so directly, but we can use a special paper having a chemical coating that’s particularly sensitive to UV. It is the same type of paper that was used with blueprint machines using a UV lamp and ammonia fumes to copy drawings made on transparent paper.
How to Make a UV-Sensitive Box Camera:
For our box camera we’ll use a very special paper, a lens, and plain tap water, and a box. The paper is inexpensive as is the lens, and the cardboard box is free-for-the-finding. Read the rest of this entry »
April 2, 2010
by: Ron Perkins
An eddy current is a current set up in a conductor in response to a changing magnetic field. Lenz’s law predicts that the current moves in such a way as to create a magnetic field opposing the change; to do this in a conductor, electrons swirl in a plane perpendicular to the changing magnetic field. Because the magnetic fields of the eddy currents oppose the magnetic field of the falling magnet; there is attraction between the two fields. Energy is converted into heat.
This principle is used in damping the oscillation of the lever arm of many mechanical balances. At the end of the arm a piece of flat aluminum is positioned to move through the magnetic field of a permanent magnet. The faster the arm oscillates, the greater the eddy currents and the greater the attraction to the permanent magnet. However, when the arm comes to rest, the attraction is negligible. Read the rest of this entry »