# maximum current a resistor can take

Discussion in 'General Electronics Discussion' started by wojnarj, Jan 23, 2014.

1. ### wojnarj

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Dec 15, 2013
here is a question from the book I mentioned in my last question:

What is the maximum current that a 220 ohm can safely handle if the power rating is 1/4 watt?

P=VI

P=I^2 * R

P=V^2 /R

so which one do I use

thank you again

2. ### Harald KappModeratorModerator

11,993
2,809
Nov 17, 2011
You have P, you have R, you don't have V.
You're looking for I.
That should guide you to the right equation.

5,164
1,087
Dec 18, 2013
I think people might assume you know how to transpose formula. If you do ignore this.

You need the formula from above P=I^2*R. You want I so you have to remove R and the^2 on I. To do this divide both sides of the equation by R which means R can disappear from along side I^2.

This now becomes P/R=I^2. You now are only left to get rid of the squared part of I. You do this by taking the square root of both sides of the equation. So this becomes Sqrt(P/R)=I

Thanks

4. ### wojnarj

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Dec 15, 2013
Thank you

I thank everyone for helping understand the formulas and when to use which one. I am not the best at transposing formulas; sometimes I get it without thinking and 70% of the time, I am banging my head 100% of the time

I will be posting more problems; that and death I am 100% sure about..

thank you
Jason