### Re: An equation or method to measure the strength of an electromagnet?

Date: Tue Mar 2 21:13:19 1999
Posted By: Bob Novak, Other (pls. specify below), Sr Process Research Engineer, Carpenter Technology
Area of science: Physics
ID: 919037233.Ph
Message:
```
Hi Jordan,

You could measure the strength of an electromagnet by hanging small iron
weights from the magnet.  When the applied weight (force of gravity acting
on the weights) exceeds the force of the magnet, the weights will fall
off.  Steel Flat washers of the same diameter as the coil would be
inexpensive and simple to use.  You can weigh several washers on a food
scale and calculate the average weight of each washer.

The equation for the magnetic field strength, H0, in Ampere-turns per
meter for an empty (air) coil is:
H0 = the applied voltage / (the number of turns of wire in the coil
winding X Area within the coil winding X the permeability of air).
The area is pie X D squared/4, where D is the diameter of the coil winding
in meters.
The permeability of air,  , is 4 X pie X 10 to the - 7  henry/meter

The Equation is for a direct current.  An alternating current applied to
the coil cannot be used for lifting magnetic objects.

By substituting different numbers for the applied voltage, the number of
turns of wire and the diameter of the coil, you can calculate how each
parameter will effect the strength of the magnet.

Electromagnets can be fun, however,  keep them away from recorded tapes or
they will erase the contents.

Enjoy that project,
Bob Novak
Specialist, Process R&D
Carpenter Technology

```

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