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-   -   Why does the E-field of radiation vary with inverse distance? (http://www.physicsforums.com/showthread.php?t=675114)

Fyreth Feb28-13 04:19 AM

Why does the E-field of radiation vary with inverse distance?
 
Feynman_Lectures_on_Physics_Volume_1_Chapter_28

In 28-2 Radiation Feynman starts talking about the third term of Eq. 28.3 and why that it varies with the inverse of the distance. On page 28-4 he says that the unit vector e'r is pointed to the apparent position of the charge. I understand that. The unit vector is just the normalized distance vector between the apparent position of the charge and the point of measurement P.
Then he says that the end of the unit vector goes on a slight curve. I assume he means that if the tail of the unit vector is on point P and the head that vector is on a sphere with radius = 1, the head is moving in along a curve.
But what does he mean with that the acceleration has a transverse component and a radial component? Is the transverse component the change in the direction of the unit vector? And the radial vector the change in the length? But isn't the length constant since it's a unit vector? And why does the former vary with the inverse of the distance and the latter with the inverse of the square?

I've been searching on Wikipedia and Hyperphysics but I can't find anything about it. I haven't seen anything that even looks remotely like Eq. 28.3.
I just started my physics study. I'm still in my first year of university. But these lectures are so much more interesting than my other books for some reason.


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