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= The motion of a charged particle under a constant $\vec{B}$ = = The motion of a charged particle in a constant $\vec{B}$ =
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= The motion of a charged particle under a constant $\vec{B}$ = This question is an advanced level question. '''Time-reversal invariance''': if any possible motion played backwards is also a possible motion, then the system is time-reversal invariant.

= The motion of a charged particle in a constant $\vec{B}$ =

The motion of a charged particle in a constant $\vec{B}$

  1. is time-reversal invariant
  2. is not time-reversal invariant

This question is an advanced level question. Time-reversal invariance: if any possible motion played backwards is also a possible motion, then the system is time-reversal invariant.

The motion of a charged particle in a constant $\vec{B}$

  1. conserves the mechanical energy
  2. does not conserve the mechanical energy

The work energy “theorem”

The work energy theorem, $\Delta T = W$ where $T$ is the kinetic energy (and $\Delta T = T_2 - T_1$ is its change) and $W$ is the net work done on the particle, is

  1. always valid (in classical mechanics).
  2. valid only for conservative forces.