# What is the electrical difference between rolled and unrolled extension cables? [closed]

I am talking about the extension cord of length 10 meter or more as follows.

The clerk said that it is better to unroll it when using. So what is the difference? I know for alternating current there will be inductive impedance for the wound cord. How to quantitatively calculate the difference? Empirical approach is also welcome!

## closed as off-topic by David Z♦Aug 21 '18 at 10:09

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• @FriendlyGhost The resistance and thermal power, $I^2R$, will be, initially, the same for both rolled and unrolled cords, but the unrolled cord has more contact with open air and will cool (dissipate the heat into the air) faster. If the rolled cord got hot, its resistance would increase, which could affect the current, etc., but that is beyond the point. – V.F. Aug 20 '18 at 16:28