A magnetic field inside the oven? The metal might have a small
residual field,
(Go back and read what I replied to. The prev. post said there was no
magnetic field inside a microwave oven)
I don't have advanced equipment here but lets assume that the earths
field is about 0.5G in the middle of my kitchen. Outdoors within 20 miles
of here, it is 0.495G or so, so I think this is accurate enough what I'm
about to do.
I hold the compass in the middle of the kitchen and note the direction of
the pointer.
Next I bring a small magnet towards the compass from what it indicates is
the east while rotating the magnet to find the orientation that causes the
greatest deflection.
When I obtain a 45 degree deflection, the magnet is making as much field
at the compass as the horz. component of the earths field. I measure this
distance and find it to be just about 4.25 inches.
We know that where I am the earths field is just about 0.5G and dipped by
about 60 degrees. This means that the magnet at 4.25 inches is producing
a field of:
0.5G * cos(60) = 0.25G
Next I place the compass inside a Panasonic microwave on a non-magnetic
book such that the compass is about 1.5 inches above the bottom of the
oven, and nearly centered. Again I observe the compass pointer and
introduce the magnet from its east until I obtain a 45 degree deflection.
I measure this distance. I comes out to be just about 2 inches.
The magnet I'm using is 0.25 inches in its largest direction so I feel
safe in using the small dipole estimate. Therefor I calculate the horz
component of the field inside the oven is:
0.25G * (4.25/2)^3 = 2.4G
Since this is the Horz component it represents a minimum for the field
value. It is a lot more than "no magnetic field" but as I pointed out not
one that will be good as a bulk eraser.
but you need a changing magnetic field to degauss the
magnetic media.
Actually you don't need a changing field if you are allowed to change the
location of the magnetic media, but that is too much of a quibble.