# How can the unit of H and J be different?

## Main Question or Discussion Point

Maxwell's equation is

∇×H=J + ...

but the unit of H is A/m while J's unit is A/m2

as quoted from wikipedia

how can it be possible?

## Answers and Replies

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phyzguy
Science Advisor
Maxwell's equation is

∇×H=J + ...

but the unit of H is A/m while J's unit is A/m2

as quoted from wikipedia

how can it be possible?
You're taking the derivative of H, and this involves dividing by a length. The components of Curl(H) has terms like partial(H)/partial(x), so there is an additional length in the denominator. This is just like the fact that the units of velocity are m/s, while the units of acceleration (which is the time derivative of velocity) are m/s^2.

i see ! thank you very much