Sketch the magnetic field lines for a finite solenoid. Explain why the field at the exterior midpoint is weak while at the interior, it is uniform and strong.

An observer to the left of a solenoid of $N$ turns each of cross-section area $\text{'}A\text{'}$ observes that a steady current $I$ in it flows in the clockwise direction. Depict the magnetic field lines due to the solenoid specifying its polarity and show that it acts as a bar magnet of magnetic moment $m=NIA$.

Draw a schematic sketch of a cyclotron. Explain briefly how it works and how it is used to accelerate the charged particles. Show that time period of ions in a cyclotron is independent of both the speed and radius of the circular path.