: I was reading the reply with interest. John,
: what in particular can cause a watch to
: become magnetised? Is it easy to do?
What are electric and magnetic fields?
Electric and magnetic fields (EMFs) are all around us. EMFs are invisible fields of energy that exist around anything that carries or uses electricity. Power lines, appliances, light fixtures and electric wiring all produce EMFs. Electric fields are produced by the voltage, or the strength of an electric charge on a wire—even when no current is flowing. Magnetic fields are produced only when a current is carrying the electric charge through a wire or conductor. Therefore, an appliance that is plugged in but not turned on will produce an electric field. When the appliance is operating, both an electric and magnetic field are present. Electric and magnetic fields quickly decrease as you move away from the source, but magnetic fields—unlike electric fields—pass through most materials and are difficult to shield.
The strength or intensity of magnetic fields are commonly measured in units called "gauss." Below are examples of magnetic fields (in milligauss; 1/1,000 gauss)
Appliance at 4 inches
Coffee Maker 2.3 to 3
Toaster 10 to 60
Iron 12 to 45
Vacuum Cleaner 230 to 1300
Hair Dryer 3 to 1400
Television 4.8 to 100
Source: Gauger, Jr., Household Appliance Magnetic Field Survey. IEEE transactions on power apparatus and systems. PA-104.
Just another good reason to stay away from Vacuum Cleaners!
