What Are Retarded Time and Position in Electrodynamics?

[AriAstronomer]

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

 

[RedX]

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.