Register to reply

Retarded time

by dipole
Tags: retarded, time
Share this thread:
Apr25-12, 05:09 PM
P: 433
I have a quick question about the retarded time when dealing with moving charges.

The retarded time is:

[itex] t' = t - \frac{r}{c}[/itex]

where [itex] r [/itex] is the distance between the point of observation and the position of the charge.

My question is very simple, is [itex] r [/itex] a function of the normal time [itex] t [/itex], or the retarded time [itex] t' [/itex]?

That is, which equation is correct?

1. [itex] t' = t - \frac{r(t)}{c}[/itex]

2. [itex] t' = t - \frac{r(t')}{c}[/itex]

Phys.Org News Partner Physics news on
Physicists unlock nature of high-temperature superconductivity
Serial time-encoded amplified microscopy for ultrafast imaging based on multi-wavelength laser
Measuring the smallest magnets: Physicists measured magnetic interactions between single electrons
Apr26-12, 01:05 AM
Sci Advisor
P: 2,470
Depends on which one is moving. If the observation point stays still, and the charge is moving, then you are interested in r(t'), the distance at time the signal was emitted.

More generally, suppose both the charge and observation point are moving, with rc and ro being positions of charge and observation point respectively relative to some fixed origin. In that case, the distance traveled by the wave will be function of both.

[tex]t' = t - \frac{||\vec{r}_c(t')-\vec{r}_o(t)||}{c}[/tex]

Register to reply

Related Discussions
Retarded time approximation Classical Physics 2
Question on retarded time. Classical Physics 1
Retarded Time Classical Physics 1
Retarded time Special & General Relativity 13
Gradient equation with retarded time Introductory Physics Homework 11