Jeff wrote in :

E cross H in mathematical terms.


'Cross product' of E and H? As in, related to 'dot product'? If so that might
be my wau in to understanding Maxwell, I've used dot product before,
translated myself to find intersections of lines, and saw cross product
closely related, documented pretty much beside it a couple of times.

On 09/11/2014 18:07, Lostgallifreyan wrote:
Jeff wrote in :

E cross H in mathematical terms.


'Cross product' of E and H? As in, related to 'dot product'? If so that might
be my wau in to understanding Maxwell, I've used dot product before,
translated myself to find intersections of lines, and saw cross product
closely related, documented pretty much beside it a couple of times.




A cross product of two vectors is a third vector orthogonal to the first
two. In the case of the EM wave, the E and H vectors are orthogonal so
the cross product is in the third dimension, the direction of propagation.

A dot product is a scalar quantity, ie it has magnitude but no
direction. As you say, it is used to find where lines, represented as
vectors, intersect.

On 2014-11-09 20:00:10 +0000, Brian Reay said:

On 09/11/2014 18:07, Lostgallifreyan wrote:
Jeff wrote in :

E cross H in mathematical terms.


'Cross product' of E and H? As in, related to 'dot product'? If so that might
be my wau in to understanding Maxwell, I've used dot product before,
translated myself to find intersections of lines, and saw cross product
closely related, documented pretty much beside it a couple of times.




A cross product of two vectors is a third vector orthogonal to the
first two. In the case of the EM wave, the E and H vectors are
orthogonal so the cross product is in the third dimension, the
direction of propagation.

A dot product is a scalar quantity, ie it has magnitude but no
direction. As you say, it is used to find where lines, represented as
vectors, intersect.

Does a rotating magnet in vacuo (no conductors around to carry current)
produce an electric field? Sounds a simple question, which has been
answered each way by several people. Anyone who is interested but not
absolutely sure should go and check this question out, I think.
Starting to try to do so illustrates the well-known fact that there is
a lot of nonsense on the web. I take it you are firmly in the 'no'
camp, Brian?



--

Percy Picacity

Brian Reay wrote in :

A cross product of two vectors is a third vector orthogonal to the first
two. In the case of the EM wave, the E and H vectors are orthogonal so
the cross product is in the third dimension, the direction of propagation.


Ok, thanks. This reminds me of the Flemings 'hand rules', which I have never
been taught directly so have failed ot remember and have to look up on the
rare occasion I need to. Any relation? Or are those limited to motors and
generators?