The term 'field' is used to describe a region where an entering item may experience a force. Magnetic fields are regions where magnetic materials will experience a force in a particular direction. Magnetic field strength is measured in tesla. However, most magnetic fields are more appropriately measured in milli-tesla. The symbol for magnetic field strength is B. There are strict conventions regarding the drawing of magnetic fields.

• magnetic field lines show the direction of the force exerted on an isolated north pole

• the proximity of the field lines indicates the relative strength of the field. Sparse lines represent weak fields. Dense lines represent strong fields

• the direction of the force on an isolated north pole is given by the tangent to the field line at any point

• crosses are used to show magnetic field lines going into the page

• dots are used to show magnetic field lines coming out of the page

Since magnetic field lines show the direction that an isolated north pole would be forced to move, they always run from the north pole of a magnet to its south pole. Familiarize yourself with the structure of common magnetic fields such as bar magnets.