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". 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 vacuum tubes (including cathode-ray tubes) it is the negative terminal where electrons enter the device from the external circuit and proceed into the tube's near-vacuum, constituting a positive current flowing out of the device. 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, the cathode is the negative terminal at the pointed end of the arrow symbol, where current flows out of the device. For example, reversing the current direction in a Daniell galvanic cell converts it into an electrolytic cell where the copper electrode is the positive terminal and also the anode.
Phototransistor anode cathode generator#
For example, the Daniell galvanic cell's copper electrode is the positive terminal and the cathode.Ī battery that is recharging or an electrolytic cell performing electrolysis has its cathode as the negative terminal, from which current exits the device and returns to the external generator as charge enters the battery/ cell. It is continued externally by electrons moving into the battery which constitutes positive current flowing outwards. This outward current is carried internally by positive ions moving from the electrolyte to the positive cathode (chemical energy is responsible for this "uphill" motion). Whether the cathode is negatively polarized (such as recharging a battery) or positively polarized (such as a battery in use), the cathode will draw electrons into it from outside, as well as attract positively charged cations from inside.Ī battery or galvanic cell in use has a cathode that is the positive terminal since that is where conventional current flows out of the device. Inside a device or a cell, positively charged cations always move towards the cathode and negatively charged anions move towards the anode, although cathode polarity depends on the device type, and can even vary according to the operating mode. The electrode through which conventional current flows the other way, into the device, is termed an anode.Ĭonventional current flows from cathode to anode outside of the cell or device (with electrons moving in the opposite direction), regardless of the cell or device type and operating mode.Ĭathode polarity with respect to the anode can be positive or negative depending on how the device is being operated. For example, the end of a household battery marked with a + (plus) is the cathode. Consequently, the mnemonic cathode current departs also means that electrons flow into the device's cathode from the external circuit. Electrons have a negative electrical charge, so the movement of electrons is opposite to that of the conventional current flow. A conventional current describes the direction in which positive charges move. This definition can be recalled by using the mnemonic CCD for Cathode Current Departs. Positively charged cations move towards the cathode allowing a positive current i to flow out of the cathode.Ī cathode is the electrode from which a conventional current leaves a polarized electrical device.
Electrode where reduction takes place Diagram of a copper cathode in a galvanic cell (e.g., a battery).
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