- #1
Vrbic
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- 18
Homework Statement
Without introducing any coordinates or basis vectors, show that, when a charged particle interacts with electric and magnetic fields, its energy changes at a rate $$\frac{dE}{dt}=\vec{v}\cdot \vec{E} $$
Homework Equations
##E_{kin} + E_{pot}= En =## const (1)
##E_{pot}=\vec{r}\cdot\vec{E}## (2)...suppose homogenic electric field and also that magnetic field does not affect magnitude of velocity. ##E## describes electric field
The Attempt at a Solution
First of all I suppose they ask on kinetic energy. Total energy is conserved. Then I put (2) in (1) and differentiate to get:
$$\frac{dE_k}{dt}=-\frac{d}{dt}(\vec{r}\cdot\vec{E}). $$
I hope, a minus sign vanish in opposite definition of vectors \vec{r}. I hope in homogenic electric field is ##\vec{E}=##const. than
$$\frac{dE_k}{dt}=\vec{v}\cdot\vec{E}. $$
Is it allright?