What Are Retarded Time and Position in Electrodynamics?

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Retarded time in electrodynamics is defined by the equation t = t_r + r/c, where t represents the present time, t_r is the time elapsed since the electromagnetic signal reached the observation point, and r/c is the time taken for that signal to travel. The retarded position w(t_r) indicates the location of a particle at the moment the electromagnetic information first arrived, which may differ from its current position w(t). This distinction is crucial for understanding how electromagnetic interactions propagate through space and time. Clarifying these concepts is essential for accurate analysis in electrodynamics. Understanding retarded time and position is fundamental for grasping the behavior of particles under electromagnetic influence.
AriAstronomer
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Hey everyone,
Just a quick question about a few electrodynamic concepts:

1) retarded time: t = t_r - (curly)r/c. Is t = total time, t_r = time elspased since the electromagnetic 'news' reached the point in question, and r/c = time taken to reach the point in question?

2) I'm a bit confused about w(t_r), the retarded position. Is this the position of a particle when some electromagnetic 'news' first reached it, and is now currently at a different position? How does it differ from w(t)?

Thanks.
Ari
 
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Your 1st equation should be:

t=t_r+r/c

where t is the present time, t_r was the time r/c ago from the present time.

w(t_r) stands for the position of a particle at a time r/c before the present time.
 
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