Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

More turns -> stronger field
more turns -> longer copper wire
longer copper wire -> more resistance(ohm)

at what turn does the resistance make the electromagnet weaker? - I want to make an ideal electromagnet.

(Sorry for being vague but I'm looking for some kind of formula or an example)

share|improve this question

1 Answer 1

up vote 1 down vote accepted

You need to combine some equations, lets list them:

Whe asume that you want the formula in terms of potential diferential, with Ohm's Law, $\Delta V = I R$, and the magnetic field inside one solenoid:

$$ B = \frac{N}{L}\mu I = \frac{N}{L}\mu \frac{\Delta V}{R} \quad\quad (1) $$

where $N$ , $L$, $\mu$, stand for the number of turns, lenght of the solenoid and magnetic permeability of you core respectively. Then we also know the dependance of $R$ over the lenght of the wire, $R = \rho\frac{l}{A}$, where $\rho$ is the resistivity, $A$ the cross section of the wire and $l$ the lenght. We can compute the lenght by:

$$ l = 2\pi rN $$

so if we subtitute the last equations in $(1)$:

$$ B = \mu\frac{N\Delta V}{L}\frac{A}{\rho 2 \pi r N } = \mu\frac{\Delta V A}{2 \pi \rho r L} $$

surprisingly it doesn't care the number of turns!!

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.