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Best way to learn Ohm's Law?

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E=IR is Ohm's Law.

Voltage equals current times resistance

Then the various versions are derived from that.

I = E/R (Divide both sides of the formula by R)

R = E/I (Divide both sides of the original formula by I)

E = IR is burned into the brain

My truck battery went dead overnight a couple of days ago. I put it on the charger, thinking the battery is toast but wanted to see if there's a short in the wiring that drained it. I watched for and saw a little spark jump when I disconnected and reconnected the negative terminal. The computer and anti-theft circuits draw juice from the battery in all newer vehicles. So I needed to measure the current, 'I', that the truck is drawing from my battery when it is sitting in the driveway. I don't have an ammeter that will read milliamps. I took a ceramic 330 ohm resistor, R, out of my box of R's and clipped my voltmeter across it, set to measure low DC voltage. With the resistor jammed between the negative terminal and the battery post, I measured 8.8 volts being drawn thru the 330 ohm resistor.

I = E/R = 8.8 volts divided by 330 ohms = 0.0266 amps

That's a pretty small load on a car battery, where we talk bout 100's of cranking amps. So I've declared the truck OK, the battery too weak to keep the computer alive. We need to keep a good battery in the vehicle nowadays. Anyway, that's Ohm's Law.

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