Thursday, 12 May 2016

Why is DC Voltage called Direct Current ?


I have had this question since a long time, and didn't find any other place to ask this. So thought will just ask here.


The "DC" in DC Voltage/Supplies stands for Direct Current. So why is it combined with Voltage in the name ?


From what I understand it might have something to do with a supply or voltage which has a constant current at one level. Is that the reason ?



Answer



The Name


With a constant load, DC (direct current) has a constant current and voltage.


This is as opposed to AC (alternating current) which, with a constant load, has an alternating current and voltage.



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It's essentially a description of the current and voltage's relationship to time. For DC, the frequency is equal to zero, not changing in time. While AC has a frequency equal to not zero, it changes with time.


Relationship between Voltage and Current


The key to the relationship between current and voltage, is the load, or resistance. This comes from Ohm's Law, \$V = IR\$. As you can see, if \$R\$, the resistance is constant then voltage (\$V\$) is equal to the current (\$I\$) times a constant coefficient. Set \$R = 1\$ and the relationship is quite obvious.


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