Thursday, 21 December 2017

capacitor - Why do farads multiplied by ohms produce a result that has a unit of seconds?


Why is the time constant (RC) measured in seconds even though the units are farads x ohms?



This is to fulfill my own curiosity as I haven't had much luck at finding the answer. I would be most grateful if someone could give me a solid answer or send me in the right direction.



Answer



It's the way the units work out.


Broken down to its form in SI units, a volt is


V=kgm2As3


where A is amperes. So, when you divide by current to get ohms, you see that


Ω=kgm2A2s3


A farad is:


F=s4A2m2kg


So when you multiply Ohms by Farads, you're left with seconds:



ΩF=kgm2A2s3s4A2m2kg=s


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