Solar Storms and You!

Activity 9: A Soda Bottle Magnetometer...Mark 2

The magnetometer design which appears as the main element of the classroom activity has two major advantages; it can be constructed from inexpensive components, and it uses a common high-intensity lamp as a light source. There are however, several disadvantages. It is very delicate because the sensing element ( the soda bottle system ) can be easily tipped over or disturbed .It also uses a light source that requires dark conditions to see the reflected spot in the wall, and the spot is not well-focussed.

With a little bit of tweaking, the design can be greatly improved. In the Mark 2 design I will describe here, the soda bottle system is bolted to a baseboard which can be clamped to a table to secure it. The light source is replaced by a laser pointer. This later substitution may be a problem for schools that forbid the use of lasers by students or teachers. We will discuss a non-laser light source that will also work in its place.

Have a look at the following picture gallery to see how the design was changed.

Picture 1 Picture 2 Picture 3
Picture 4 Picture 5 Picture 6

  1. The base consists of two pieces of 3/4-inch pine measuring 1 foot on a side.
  2. I used a 2-inch 'cookie cutting' drill bit to drill a centered hole in the top piece.
  3. The punched-out disk was then glued to the center of the bottom piece.
  4. What you now have when you put the two pieces together is a bottom piece that is fixed, and a top piece that is free to rotate parallel to the bottom piece when sandwiched together.
  5. Now cut a 2-inch x 2-inch piece of pine, and with the two base pieces sandwiched together, glue the 2x2 piece to the punched-out plug.
  6. After this dries, you will then have the two base pieces free to rotate, but not free to fall apart!
  7. Next, drill a 1/4 inch hole in the center of this 2x2 inch 'pedestal and drill or file a similar hole in the bottom of the soda bottle used in the original magnetometer design
  8. With a 2 1/2-inch by 1/4 inch bolt, you will attach the soda bottle to the center of the wood base

What you now have is a soda bottle whose orientation is determined by the position of the bottom wood base piece, and an upper deck that is free to rotate around the soda bottle without moving the soda bottle. The next step is to fix the light source on the top plate.

The particular method you chose will depend on the kind of light source you use. For a cylindrical laser pointer with a 'momentary-contact' on/off switch on its barrel, I simply designed a pedestal which was glued to one corner of the movable top base plate. the laser pointer was secured with wood wedge so that depressing the on/off switch did not disturb the light beam by more than its own diameter. Laser pointers can be purchased from companies such as Edmund Scientifics in Barrington New Jersey for under $30.00.

If you use something other than a laser pointer, such as a small penlight flashlight, you will have to experiment with finding a mounting that best suits the geometry of your light.


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