Category Archives: Electromagnetism
I was just discussing the different definitions that some JCs give for the definition of the Tesla (the SI unit for magnetic flux density) with my JC2 students last week. According to the 'A' level examiners, they are looking for something more like:
The magnetic flux density of a magnetic field is said to be 1 Tesla, if the force acting per unit length on an infinitely long conductor carrying a current of 1 A and placed perpendicularly to the magnetic field is 1 N m-1.
Rather than what is found in some A-level guide books:
A tesla is the magnetic flux density if a force of 1 N acts on a wire of length 1m, carrying a current of 1A placed perpendicular to the magnetic field.
Some JCs still teach this erroneous definition in their lectures.
So, why is the second definition wrong? In the measurement of a tesla, if we refer only to a wire of finite length, due to the end effects, the magnetic flux density at both ends of the wire will not be the same as that in the middle.
I will be addressing this error and more in my upcoming June holiday Physics intensive workshop meant for JC1 and JC2 students. Do sign up early to avoid disappointment!