9454Views9Replies

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

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.

Tags:

## Discussions

The forums are retiring in 2021 and are now closed for new topics and comments.

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.

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

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.

A car battery has 500 amps and up. Where would your 12 volts go if you loose a volt for every amp

I use a 10 ohm resistors on a 9 volt battery as an ignitor for rocketry. Sometimes numbers are just numbers

You are no doubt way past all this, but OHMITE makes great load resistors that will handle the kind of power you are talking about. 144 watts, but you know that already.

What resistor would I need to drop 6 volts to 4.5 volts?