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| Magnetometer - Measuring the magnetic field of Earth |
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Photo Cell Magnetometer
This project is a simple approach in measuring disturbances in Earth's magnetic field.
It is simple, but produces neat results.
The bar magnet is suspended on a steel guitar string about 0.008 inches in diameter.
Normally the magnet will line up with the Earth's magnetic field as any compass
would and point North and South. The top end of the guitar string must be fastened
so that it can be rotated to wind up the guitar string to produce enough torque to
force the magnet to point East and West instead of the North-South position it would prefer.
It thus becomes a torsion balance in which its East-West position is balanced against the Earth's magnetic
field. So long as the Earth's magnetic field remains constant the magnet remains
stationary. Charged particles from solar flares set up currents in the magnetosphere
that change the strength of the magnetic field and therefore the position of the
balanced magnetic compass needle.
The drawing on the right shows how the shadow strip shades two Cadmium Sulfide photo cells
equally from light from the bulb above them. Their resistance depends on how much light falls
on them and so long as they are lit equally the Wheatstone bridge shown below the drawings
remains balanced. During a magnetic storm the torsion balance is moving the shadow strip and
causes different illumination of the CdS cells. The Wheatstone bridge is unbalanced and the
signal can be measured at the output.
The balance is stabilized by a plate (i.e. part of a Coke tin) dipped into oil (normal car oil will do) in order to
damp all sort of environmental vibrations.
Left: front view - right: top view
LINKS:
Photo cells Magnetometer
Photo cells Magnetometer #2
Last-Modified: Mon, 07 May 2007 18:00:31 GMT
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