The potential difference (emf) between the ends of the bar is 10 V. The polarity is as shown in Figure 10.4c. The polarity
can be deduced from the direction of the field E ¼ v B or from the fact that the magnetic field exerts a force on the
electrons which moves them upward. This bar can now be used as a source in a circuit, and in this sense, the motion in
the field makes the bar a generator.