Final answer:
The negative electrode of an electrotherapy device is called the cathode in an electrolytic cell and is marked with an 'N' or a minus sign.
Step-by-step explanation:
The negative electrode of an electrotherapy device is typically referred to as the cathode. This term can be a bit confusing because the polarity of the cathode depends on the type of electrochemical cell. In electrolytic cells, which are non-spontaneous and require an external current, the cathode is actually negative, contrary to what one might expect.
It is marked with an 'N' or a minus '-' sign to indicate its negative charge. On the other hand, in voltaic cells, which are spontaneous, the anode is negative and the cathode is positive. It is essential to note that electrons flow from the anode to the cathode regardless of the cell type.
In an electrochemical cell, the anode is negative and the cathode is positive. However, in an electrolytic cell, the anode is positive and the cathode is negative. Therefore, the negative electrode of an electrotherapy device would be the anode.