[vox-tech] ohms law

[Chris Jenks]

On Fri, 2 Feb 2007, Jimbo wrote:
> [...]
> I am a mechanic by trade.  I am good at diagnosing electrical and 
> drivability.  I have seen a few times that high resistance in the negative 
> leg of a circuit can take out components like computers, modules and even 
> not-so-complicated devices like bulbs and switches.  What I don't understand 
> is why.  Ohm's law states that E=IXR.  If this is the case then if resistance 
> is high it will decrease amperage.  I would tend to think that just the 
> opposite would happen...component would just lose power and not fry.

   Dear Jimbo,

   You're right that the current should drop if the total resistance 
increases, since the battery voltage is practically fixed. My thought 
while I was reading this was that noise in the circuit, from say corrosion 
at the negative battery connection, could explain the failure of 
components. Unlike any other type of device I can think of, some electric 
motors can burn out if they aren't getting enough power because they cool 
themselves while turning. On the other hand, incandescent light bulbs will 
last a very long time if run at less than their full operating voltage 
(such as a 220 volt light bulb run at 110 volts). I would also expect the 
part of the circuit causing the resistance, such as a frayed cable, to get 
hot and burn out in that place, since power = EI = RI^2

   Yours,

     Chris