If you place a 1 ohm resistor across a 12 volt car battery, how much power will it dissipate?

This is one of the exercise from the book, "The Art of Electronics." They do not give answers and i wanted to know if i did it right. I got the answer of 1.44 watts, but i am not sure if this is correct.

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rickharris2 years ago

Using ohms law:

I=V/R

then 12/1=12 amps.

Watts =V * A

so 12 * 12 = 144 watts.

We would expect a 1 ohm resistor to draw a LOT of amps and so dissipate a lot of power.

Your answer works for a 100 ohm resistor though

12/100 = 0.12 amps

0.12 X 12 = 1.44 watts.

That's only partially correct because most resisitors would catch fire after less than 5 seconds...

Unless you have a 150 Watt resistor, Which I don't know, but I'm guessing they aren't sold as 1ohm

cooldude01 (author)  rickharris2 years ago

Thanks. I had got both answers but i didn't think it was 144 watts because it was so high. Alright thanks lets me know i am on the right track.

Nooo! A 1 ohm resistor is practically a short circuit! It will only drop a volt for every amp of current flowing through it! You can check out my videos about ohms law and watts law and series/parallel circuits on youtube, under the channel Power Max if you're intrested.

It's often useful to take circuits to mental extremes. for example we all know that a total short circuit would draw as much current as the power source can supply. 1 Ohm is not far from that short circuit so the answer is going to be high.