- #1

TerryW

Gold Member

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## Main Question or Discussion Point

Can anyone help me with Ex 4.1 in MTW?

What is a 'generic' field? My expectation is that it would comprise an Electric Field, with arbitrary direction, a Magnetic Field, also with arbitrary direction, and a radiation field (E and B of equal magnitude) , radiating in an arbitrary direction.

Trying to put this together however to get the Poynting density of energy flow and the density of energy is a bit of a mess however, so I suspect my expectation is wrong.

Moving on to the next bit of the problem, if you do define the unit vector

Can anyone help?

TerryW

What is a 'generic' field? My expectation is that it would comprise an Electric Field, with arbitrary direction, a Magnetic Field, also with arbitrary direction, and a radiation field (E and B of equal magnitude) , radiating in an arbitrary direction.

Trying to put this together however to get the Poynting density of energy flow and the density of energy is a bit of a mess however, so I suspect my expectation is wrong.

Moving on to the next bit of the problem, if you do define the unit vector

**and velocity parameter α as shown, then a solution to this is a radiation field with E along the x axis, B along the y axis, producing a Poynting vector along the z axis. If you then translate to the rocket frame,***n***E**X**B**disappears because**B**becomes zero, not because**B**becomes parallel to**E**. I can't see how**B**ends up parallel to**E**.Can anyone help?

TerryW