# Time it takes to reach maximum current?

While studying inductors, I learned that it will take some time for current to reach it's rated value $I$, and considered in "steady state".

Is the same applied for singular wires(not forming a loop/multiple turn loop)? In general, if a wire with low resistance and possibly low inductance had DC flowing, will it time a short duration of time to reach maximum current? Using this equation: $t = \frac {L}{R}$.

From the equation above, that's the time it takes for current to reach $\frac {2}{3}$ it's value?

• Can you please clarify what you mean by "not form a loop"? A loop and a coil are separate concepts. Draw a picture if that helps. – Wossname Sep 17 '16 at 11:09

Is the same applied for singular wires(not forming a loop/multiple turn loop)?

The example you ask for consideration is an imposibility. If a wire passes current then it MUST have a return path to the signal source and this forms a loop. Even a monopole antenna passes current and has a return path even though physically it looks like a wire with a connector at one end.

Having made my rant, you can theoretically predict that a wire does have self-inductance and that inductance is maximum when the "return path" is a gazillion miles away: -

Where "l" is the wire length and "d" is the diameter.

From the equation above, that's the time it takes for current to reach 2/3 it's value?

No, it's not two thirds it's 0.63212055882 or $1-e^{-1}$

• I wonder if the OP should have used the term "form a coil" instead of "form a loop". A coil will experience a slower rise time (due to back-EMF in adjacent turns of wire) than a straight section of wire all other factors being equal. Straight sections of wire (such as a trace on a PCB) will have a rise time due to the fact that real physical circuits are subject to unwanted phenomena such as capacitance and other minor annoyances. – Wossname Sep 17 '16 at 10:56
• The OP said NOT forming a loop – Andy aka Sep 17 '16 at 11:03
• Andy, yes I think it might be a nomenclature issue. I think the OP is talking about inductors and straight wires (eg going from one terminal of a battery to the other without any formed coils in it). The OP may be using "loop" and "coil" synonymously when that might not be the intention. – Wossname Sep 17 '16 at 11:08
• I fail to see the relevance of your observation on my answer. Sorry! – Andy aka Sep 17 '16 at 11:42
• I didn't mean any offense. – Wossname Sep 17 '16 at 11:46