Definition:Ampere (Unit)/Mistake

Source Work

1964: Milton Abramowitz and Irene A. Stegun: Handbook of Mathematical Functions

$2$. Physical Constants and Conversion Factors

Mistake

The SI unit of electric current is the ampere defined by the equation $2 \Gamma_m I_1 I_2 / 4 \pi = F$ giving the force in vacuo per unit length between two infinitely long parallel conductors of infinitesimal cross-section.

Correction

No mention is made of the fact that these conductors have to be situated $1$ metre apart.

The full equation is:

$\dfrac {2 \Gamma_m I_1 I_2} {4 \pi r} = F$

where $r$ is the distance between the conductors.

Hence when the conductors are $1$ metre apart, $r = 1$ and so $2 \Gamma_m I_1 I_2 / 4 \pi = F$ can be applied.

Sources

• 1964: Milton Abramowitz and Irene A. Stegun: Handbook of Mathematical Functions ... (previous) ... (next): $2$. Physical Constants and Conversion Factors