两根电线间的电场力

When the direction of the current of two wires is in the same direction, there is always an attractive force between the two wires. When the direction of the current of the two wires is in the opposite direction, there is a repulsive force between the two wires.

Example:

$$F = IlB\sin(90)$$ $$\frac{F}{l} = I_2B_1$$ $$\int{B_1}\cdot dl = \mu_oI_1$$ $$B1 = \frac{\mu_oI_1}{2\pi r}$$ $$\frac{F}{l} = \frac{\mu_oI_1}{2\pi r}$$

$C = 2\pi r$ (distance around the circle)

$$\frac{F}{l} = \frac{(4\pi \times10^{-7})(5)(10)}{(2\pi)(0.01)} = 0.001 = 1\times10^{-3}N \cdot m$$

$1\times10^{-3}N \cdot m$ is the force of Wire I on Wire II