December 01, 1998 Filed in: Demo Corner
John Childs, Grenville Christian College, Brockville
This simple little homemade device can provide a very effective demonstration of AC current, it’s fun, and it’s cheap! All you need is a little neon lamp, a resistor and an AC cord. Solder one leg of the neon lamp in series with a 10K, 1/2 watt resistor, and then attach to the AC cord. Heat shrink tubing is excellent insulation for this construction, otherwise use carefully applied electrical tape. Be sure to insulate throughly, you have AC power here. Read More...
September 01, 1998 Filed in: Demo Corner
Peter Scovil, Waterford District High School,
At the OAPT Conference this past June at the University of Waterloo, I gave a short demonstration of a vibrator I built from a Radio Shack speaker. It allowed me to produce longitudinal as well as transverse standing waves. This is based on an idea from one of the AAPT conference workshops. Read More...
June 01, 1998 Filed in: Demo Corner
John M. Pitre, Department of Physics, University of Toronto
In the January 1997 issue of The Physics Teacher
, two articles appeared detailing the use of rare earth magnets to demonstrate Lenz’s Law in the classroom. The principle involved is that a permanent magnet falling through a tubular conductor will induce a current in the conductor and hence a magnetic field which will oppose the magnetic field of the permanent magnet and thus slow its rate of fall. This article gives variations of the methods discussed in those papers. Read More...
January 01, 1998 Filed in: Demo Corner
George Vanderkuur, WICED Centre, TDSB
Bricks, books, or metre sticks are all you need for this neat demonstration. As illustrated, the top brick projects by half its length and subsequent bricks project 1/4, 1/6, 1/8, et. Brick lengths. After n
bricks, the cantilever will project a distance of d
= 1/2 + 1/4 + 1/6 + … + 1/(2n
). This may be simplified to d
= 1/2 (1 + 1/2 + 1/3 + … + 1/n
). For four bricks, the projected distance is 1.04 brick lengths, and for n
= 5, the distance is 1.14 brick lengths (so that the top brick is clearly out beyond the edge of the table). Read More...