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The terms anode and cathode are not defined by the voltage polarity of electrodes, but are usually defined by the direction of current through the electrode. An anode usually is the electrode of a device through which conventional current (positive charge) flows into the device from an external circuit, while a cathode usually is the electrode through which conventional current flows out of ...
Townsend's early experimental apparatus consisted of planar parallel plates forming two sides of a chamber filled with a gas.A direct-current high-voltage source was connected between the plates, the lower-voltage plate being the cathode and the upper-voltage the anode.
A galvanic cell's anode is less negative, supplying less energy than thermodynamically possible. A galvanic cell's cathode is less positive, supplying less energy than thermodynamically possible. The overpotential increases with growing current density (or rate), as described by the Tafel equation .
When the pressure–gap product is high, an electron will collide with many different gas molecules as it travels from the cathode to the anode. Each of the collisions randomizes the electron direction, so the electron is not always being accelerated by the electric field —sometimes it travels back towards the cathode and is decelerated by ...
The upper graph shows the current density as function of the overpotential η . The anodic and cathodic current densities are shown as j a and j c, respectively for α=α a =α c =0.5 and j 0 =1mAcm −2 (close to values for platinum and palladium).
At the Zn anode, oxidation takes place (the metal loses electrons). This is represented in the following oxidation half reaction (note that the electrons are on the products side): + + At the Cu cathode, reduction takes place (electrons are accepted).
In a vacuum tube or a semiconductor having polarity (diodes, electrolytic capacitors) the anode is the positive (+) electrode and the cathode the negative (−). The electrons enter the device through the cathode and exit the device through the anode. Many devices have other electrodes to control operation, e.g., base, gate, control grid.
Gas flows through the ion source between the anode and the cathode. A positive voltage is applied to the anode. This voltage, combined with the high magnetic field between the tips of the internal and external cathodes allow a plasma to start. Ions from the plasma are repelled by the anode's electric field. This creates an ion beam. [83]