Ørsted's experiment
= Ørsted's experiment
{c}
A nearby compass needle changes direction when a wire carries an <electric current>. Reversing the current or exchanging above/below positions reverses the magnetic action, connecting <electric currents> with <magnetic fields>. The long-wire idealization has $B=\mu_0 I/(2\pi r)$ and circular orientation given by the <right-hand rule>.