A semiconducting device is connected in a series circuit with a battery and a resistance. Current is found to pass through the circuit. If the polarity of the battery is reversed, the current drops to zero. The device may be

The device described is a p-n junction diode. A p-n junction exhibits rectifying behavior, meaning it allows current to flow in one direction but blocks it in the other. When the battery is connected such that the p-region is at a higher potential than the n-region, the device is forward-biased, allowing current to pass with minimal resistance. Reversing the battery polarity makes the device reverse-biased. In this state, the depletion layer width increases, creating a high potential barrier that prevents majority carriers from crossing the junction. Consequently, the current drops to almost zero, as the junction offers very high resistance and only allows a negligible leakage current due to minority carriers. In contrast, individual p-type, n-type, or intrinsic semiconductors act as ohmic conductors and would allow current to flow regardless of battery polarity.