The relationship between current and current density is explained by means of several examples.
The current density and its relation with the current in a circuit is explained.
Thomson parabola method, Cyclotron motion, Determination of $e/m$ of electrons and Hall effect are discussed as examples of motion of charged particles in electric and magnetic fields.
A particle moves in a one dimensional box with rigid boundary at $x=0$ and $x=L$ walls. If a small perturbation $V_1$, given by $$ V_1 (x)=\left\{ \begin{array}{ll} \epsilon V_0 & \mbox{ for }\qquad {L\over 4} < x < {3L\over 4}\\[2mm] 0 & \mbox{ otherwise}\end{array}\right.$$ is applied, find the shift in the $\mbox{n}^{\mbox{th}}$ energy level.
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