# Larmor's formula problem

1. Dec 3, 2003

### Ed Quanta

I understand that when a point charge accelerates that it radiates energy due to the acceleration field. Larmor's formula shows the power which is radiated, and is written: P=uoq^2a^2/6(pi)c. My question is this. How can you calculate the initial kinetic energy of a point charge which is travelling at a velocity v? I understand that if the point charge is decelerating until it reaches v=0 then its kinetic energy will be less because it radiated energy away while accelerating. But I am just not sure how to numerically represent the total kinetic energy of the particle prior to decelerating. Is it just E= 1/2qv^2?

2. Dec 4, 2003

### mathman

Kinetic energy for particles going at ordinary speeds is m0v2/2.

However, when getting close to the speed of light, the kinetic energy is the difference between the total energy and the rest energy. The total energy is mc2 while the rest energy is m0c2. m=m0/sqrt(1-(v/c)2).

3. Dec 7, 2003

### Ed Quanta

Isn't 1/2mv^2=gravitational kinetic energy? If talking about the kinetic energy of an electron, wouldn't it be more accurate to talk of kinetic energy in terms of charge and velocity since charge is what causes the electric force?