Therefore 'exode' would have become inappropriate, whereas 'cathode' meaning 'West electrode' would have remained correct with respect to the unchanged direction of the actual phenomenon underlying the current, then unknown but, he thought, unambiguously defined by the magnetic reference. This made the internal current East to West as previously mentioned, but in the event of a later convention change it would have become West to East, so that the West electrode would not have been the 'way out' any more. He fundamentally defined his arbitrary orientation for the cell as being that in which the internal current would run parallel to and in the same direction as a hypothetical magnetizing current loop around the local line of latitude which would induce a magnetic dipole field oriented like the Earth's. The reference he used to this effect was the Earth's magnetic field direction, which at that time was believed to be invariant. His motivation for changing it to something meaning 'the West electrode' (other candidates had been 'westode', 'occiode' and 'dysiode') was to make it immune to a possible later change in the direction convention for current, whose exact nature was not known at the time. Previously, as related in the first reference cited above, Faraday had used the more straightforward term 'exode' (the doorway where the current exits). The use of 'West' to mean the 'out' direction (actually 'out' → 'West' → 'sunset' → 'down') may appear unnecessarily contrived. In that paper Faraday explained that when an electrolytic cell is oriented so that electric current traverses the 'decomposing body' (electrolyte) in a direction 'from East to West, or, which will strengthen this help to the memory, that in which the sun appears to move', the cathode is where the current leaves the electrolyte, on the West side: ' kata downwards, `odos a way the way which the sun sets' (, reprinted in ). The word was coined in 1834 from the Greek κάθοδος ( kathodos), 'descent' or 'way down', by William Whewell, who had been consulted by Michael Faraday over some new names needed to complete a paper on the recently discovered process of electrolysis. In a cathode ray tube, it is the negative terminal where electrons flow in, i.e., where current flows out of the device.Īn electrode through which current flows the other way (into the device) is termed an anode.Note electrode naming for diodes is always based on the direction of the forward current (that of the arrow, in which the current flows 'most easily'), even for types such as zener diodes or solar cells where the current of interest is the reverse current. In a diode, it is the negative terminal at the pointed end of the arrow symbol, where current flows out of the device.In a recharging battery, or an electrolytic cell, the cathode is the negative terminal, which sends current back to the external generator.It is continued externally by electrons moving inwards, negative charge moving one way amounting to positive current flowing the other way.

This outwards current is carried internally by positive ions moving from the electrolyte to the positive cathode (chemical energy is responsible for this 'uphill' motion). In a discharging battery or galvanic cell (drawing) the cathode is the positive terminal, where conventional current flows out.To dispel a common misconception, often incorrectly inferred from the correct fact that in all electrochemical devices positively charged cations move towards the cathode and/or negatively charged anions move away from it, cathode polarity is not always negative but depends on the device type, and sometimes even in which mode it operates, as determined by the above current direction based universal definition. A cathode is an electrode through which (positive) electric current flows out of a polarized electrical device.

Diode cathode anode