E&M > Electromagnetic Induction > Induced Currents and Forces

DCS# 1C30.22

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ELECTROMAGNETIC INDUCTION AND FREE FALL

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APPARATUS

glass tube with coils	202-20-C
strong cylindrical magnet	202-20-D5
storage scope	202-08-B
sandbox	202-20-C

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DESCRIPTION

Drop the magnet through the tube.  The induced voltage looks like this:

 

NOTES

Centers of coils are 30 cm apart.

Use the sandbox to catch the magnet.  If bottom of tube is too low, magnet may bounce back and break it.

Scope settings:

0.2 V/div

50 ms/div

triggering:

single sweep mode

internal source

AC coupling

level  ~1 o'clock

Or replace the storage scope with a computer running LoggerPro.

A java applet of a magnet falling through a conducting ring, which shows magnetic field lines and monitors the eddy current, can be found here: http://web.mit.edu/jbelcher/www/java/falling/falling.html .

 

REFERENCES

J.S. Huebner and J.T. Humphries.  Am.J.Phys. 42, 870 (1974).
TPT 12 (2), 115.