Soda Bottle Magnetometer

NASA scientists have designed, for school demonstrations, a simple magnetometer (copying the Gauss variometer plan) for measuring the changes in the Earth's field.1 This soda-bottle magnetometer (Figure 5.4) is sensitive enough to detect solar-terrestrial magnetic storms. You will need:

Build the magnetometer by cutting the bottle in half about midway from its base. Then cut the index card so that when it is suspended inside the bottle it does not touch the sides. Glue the piece of soda straw to the top of the magnet, and thread the sewing thread through the straw and tie it to make a small triangular loop. Glue the mirrored sequin to the front of the index card and, with a marking pen, put a dot near its center. Glue the magnet to the top edge of the card. Tie a 1-foot piece of sewing thread to the loop of thread that goes through the soda straw. Thread the other end of this suspension thread through the inside of the top part of the severed soda bottle and through the threaded part of the bottle where the bottle cap screws on. Feed the remaining suspension thread through the inside of the bottle cap. Add the sand to the bottom half of the soda bottle. Rejoin the top part of the bottle with its bottom, making sure that the index card swings freely and that the magnet remains parallel to the floor and the tabletop. With the 2-inch-wide tape, carefully tape the top and bottom of the bottle together, making sure that the length of the suspension thread is adjusted so that the bar magnet and mirrored sequin spot hang below the tape seam.

Place the soda-bottle magnetometer on a level surface. Turn on the high-intensity lamp and, point its light toward the mirrored sequin at an angle to the mirror spot so that the light from this spot is reflected onto a wall located about 2 meters (about 6 feet) from the bar magnet. The spot that you made in the center of the mirrored sequin should be visible so that it can be used to accurately mark the pointing direction of the magnet from day to day. Some

'See the website http:// image, gsfc.nasa.gov/poetry/workbook/page9.html.

REQUIRED MATERIAL: One 2-liter clear soda bottle

One high-intensity lamp One mirrored dress sequin One marking pen 2-inch wide clear packing tape One ruler with a meter scale Super glue with cap 2 pounds sand 2 feet sewing thread One 3 x 5-inch index card One 1-inch piece of soda straw One small bar magnet

Fasten itiread to cap

Sewing Thread

Cut ^ and rejoin

Card

Mirror

Sand

Storm / Event

Storm / Event

Soda Bottle Magnetometer

Degrees >

FIGURE 5.4 ► This soda-bottle magnetometer was designed by GSFC/NASA.

spot motion

Degrees >

0.57 x dellection in cm distance in meters

FIGURE 5.4 ► This soda-bottle magnetometer was designed by GSFC/NASA.

effort may be required to find a location that is undisturbed and where this setup can be arranged so that the lamp, magnetometer, and reflected spot are in accessible positions on a table, or other flat surface, near a wall.

If the distance between the mirror and the spot on the wall is exactly 2 meters (6 feet 7 inches), a 1-cm (7/16 inch) shift in the spot location equals about a .25° change in the direction toward magnetic north. During geomagnetic storms, deflections of several degrees, lasting many hours or even days, can be seen with this device. Most of the time, however, the spot will remain in the same location. Note that if any of the parts are moved, the measurements will be affected. Moving metal or magnetized material near the magnetometer will deflect the spot.

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