# Why motion of a charged particle experences perpendicular motion in a magnetic field? Physical answer please

I understand fleming's left hand rule. But why moving charged particle is deflected? Due to the magnetic field generated by charged particle and resultant direction of that mag. field and applied magnetic field?

Pl try a non mathematical answer.

• So there are two level on which you can understand this. At one level it is simply an observed behavior—if you run the experiment that is what happens—and the math simply reflects that (right? math reflects observation, not the other way!). The deeper level requires a pretty good understanding of the mathematics of special relativity: transform to a frame where the magnetic field is zero, compute the force due to the pure electric field then transform back, and the result gives you the perpendicular motion because of the nature of the Lorentz transform and the skew-symmetric EM tensor. – dmckee --- ex-moderator kitten Feb 11 '18 at 17:34

## 1 Answer

When you apply Fleming's left hand rule, the first finger points in the direction of the field applied from outside. The field generated by the moving charge itself is irrelevant. [There are ways of picturing forces acting on currents that do involve the resultant magnetic field lines, but they are seldom used these days, and the resultant field is not what you use when applying the left hand rule.]