As demonstrated in Fig. 2.2, suppose there is magnetic field B in the air. When current I is applied to the wire placed across the field, force F is generated in the wire. The intensity of this force is given by the following equation, which is called the BLI law.
F = BLI ...... (2.1)
F: Force [N] B: Magnetic flux density [T]
L: Length of wire in the field [m] I: Current [A]
Moreover, the direction of force applied to the wire is in the direction shown in the figure according to Fleming's left-hand rule.
Regarding the corresponding relationship between your fingers and symbols, memorize it using "F, B, I" starting with the thumb, or going in reverse starting from the middle finger and moving toward the thumb using "Current, Field and Force".
Symbol B represents the intensity of magnetic field lines, and is called magnetic flux density. Magnetic field lines are not visible and therefore it is not possible to check directly. The International System of Unit (SI) of magnetic flux density is T (Tesla), which is equal to [Wb/m2] of MKS unit.
One tesla is the intensity of a magnetic field when magnetic flux of one weber [Wb] is present per square meter.
Another unit, gauss [G], is also used by physicists and magnet manufacturers. One T is equivalent to 10,000 G.