Magnets are used for a variety of applications. From your common refrigerator magnet to the magnets used in MRI machines, they can be both entertaining and practical. The strength of a magnetic field is measured in either gauss or tesla units.
Magnets come in two types: Permanent magnets will have a magnetic field no matter what happens to them. Electromagnets are metals that only have a magnetic field when an electric current runs through them. Some soft metals can become temporarily magnetized in the presence of a magnetic field, but once the field is gone, they are no longer magnetic. Standard magnets, like fridge magnets, are permanent magnets.
The strength of a magnetic field is typically measured in either gauss or tesla units. One tesla equals 10,000 gauss. Magnometers, gaussmeters or pull-testers are all used to gauge the strength of a magnet.
According to the National High Magnetic Field Laboratory of Florida State University, a fridge magnet is about 0.001 tesla. To put that in perspective, the Earth's magnetic field is about 0.00005 tesla and an average MRI magnet measures 1.5 tesla.
