A comment in another thread led me to think about an experiment which can hopefully test the validity of the pointing vector theory for a dc current.(adsbygoogle = window.adsbygoogle || []).push({});

I’m very unsure of the outcome of this experiment but what the heck. Here it goes: the Poynting theorem states E x H is power per unit surface area.

First consider a single winding with dc current I. We know that H is higher at the surface then at the centre, but E is everywhere the same running length wise. Now think of a coil made out of fairly thick wire say 10mm square with say 20 windings. Similar as with the single wire, a winding in the centre will have a smaller H field then the ones at the outside. Therefore since all winding have the same surface area, current and E field, the outside windings should get hotter than the inside ones. Therefore 2 small thermocouples should be able to pick up the differential.

Note however that the middle one will very quick receive thermal energy from the surrounding wires.

Any thoughts?

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Poynting proof for a dc current?

**Physics Forums | Science Articles, Homework Help, Discussion**