![]() In the electron gun shown, if the accelerating voltage is connected the right way round, the heated cylinder is the cathode, and the perforated electrode through which the electron beam emerges is the anode. In other words, inside the device conventional current is from anode to cathode (so outside the device, in accordance with Kirchhoff's first law, it is from cathode to anode). ![]() In any device (for example battery, electrolytic cell or diode) the anode is the electrode towards which, inside the device negative charge carriers flow, or away from which positive charge carriers flow. "the anode is the source of electrons to the external circuit and the cathode is the sink." ( source)Ĭan anyone provide an explanation suitable for intermediate level physics undergrads that explains why the anode is positive in this case?."The anode is the positively charged electrode The anode attracts electrons or anions" ( source).So why is the positive terminal the anode here? But in this case, we don't have an electrolytic or galvanic cell. It appears that fundamentally (at least in chemistry), the question of which terminal is labeled "anode" has to do with where oxidation occurs. Some cursory research (for example this chemistry stack exchange question) makes it clear that this is a complicated issue. ![]() This leads to some student confusion, because they are used to the anode of the battery being the negative terminal. In this image taken from the manual of the NaRiKa/Nada Scientific EM-4N e/m apparatus, you can see that the positively-charged electrode (the one electrons are attracted to) is labeled "anode." ![]()
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