PHYS-E0461 - Introduction to plasma physics for fusion and space applications D, Lecture, 13.9.2021-15.12.2021
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Food for thought #2
Let’s consider the significance of Earth’s magnetic field on Earth’s
surface. Put an electric charge in between two capacitor plates that
produce a strong electric field with straight field lines perpendicular
(East-West) to the prevailing (weak) Earth’s magnetic field. According
to common sense (and experience), the particle is accelerated towards
one of the plates. However, during the lectures we learned that if the
particle experiences electric and magnetic fields perpendicular to each
other, it moves in direction perpendicular to both fields, i.e., up or
down in this case! What makes things even stranger is that the magnitude
of the drift is given by E/B, i.e., it is particularly strong for LOW
magnetic fields. Consider carefully the motion of the particle and show
that there is no contradiction and the particle follows the electric
field.