We developed teaching materials about the flow-direction and the characteristic of the cationic ray in vacuum. In general, Crookes tube uses plate-shaped electrodes for observation of the flow-direction of the electron ray. By the use of needle-shaped electrodes instead of plate-shaped ones, the purplish-red color discharge was generated in the low vacuum and the impeller was rotated toward the cathode from the anode opposite to the case of Crookes tube. This phenomenon is considered to indicate that the cationic particles collided with the surrounding neutral ones and those gained larger momenta, as a result of continuous collision. Thus, it was observed that the purplish-red color discharge was deflected to the direction of the Lorentz force by the use of magnet. It is expected that our teaching materials are effective in promoting the observation and understanding the relationship between the current flow and the magnetic field.
