tesla, T
is: the SI unit of magnetic field strength.
is defined: by 
So, a uniform magnetic field has a strength 
of 1 tesla, if a particle with a charge of 1 coulomb moving with a speed of 1 metre per second in a direction perpendicular to that field experiences a magnetic force of 1 newton. Alternatively (and equivalently), a uniform magnetic field has a strength of 
if a wire carrying a current of 
in a direction perpendicular to the field experiences a force of 1 newton per metre length of wire, so 
[P4.2, P4.3]
is exemplified: by the magnetic field near a typical bar magnet, which has a strength of about 
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