Neon lamps are utilized to measure electrical polarity due to their glow discharge mechanism, which is dependent on the polarity of the applied voltage. When connected to a DC source, only the negatively charged electrode, or cathode, emits light, indicating the direction of current flow. This phenomenon occurs because the ionization of neon gas creates a plasma state, allowing electrons to flow from the cathode to the anode. In contrast, with an AC source, both electrodes will glow alternately during each half cycle.
PREREQUISITESElectronics enthusiasts, electrical engineers, and students studying electrical circuits and plasma physics will benefit from this discussion on neon lamp polarity measurement.
DaTario said:My problem with your answer is that I have the ideia that, in simple electric circuits, when the current starts, I used to think that the current will be established in all positions basically at the same time, and not only near the negative pole of the battery. Thus, it seems reasonable to me that, in a discharge lamp, when the negatively charged electrode starts sending its electrons, the glow would appear also in all positions of the electron's path to the positively charged electrode.
When driven from a DC source, only the negatively charged electrode (cathode) will glow. When driven from an AC source, both electrodes will glow (each during alternate half cycles).