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### Why is radiation power defined at infinity?

There is usually a "near field" part of the field energy that falls off faster than $1/r^2$. I suppose the $r\to \infty$ in Griffiths is designed so as not to count this part of the ...
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1 vote
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### How do I calculate change in flux in an augmented rail accelerator without violating conservation of energy?

Considering only an idealized model where the rails and the projectile are both 1-dimensional, straight wires. Start with the Lorentz force $\mathbf{F}=q(\mathbf{E}+\mathbf{v}\times \mathbf{B})$. ...
• 2,133
1 vote

### Why is radiation power defined at infinity?

Just adding to @mike stone From: https://en.wikipedia.org/wiki/Dipole#Dipole_radiation, the fields from an oscillating ($\omega$) electric dipole ($\vec p$) is:  \vec E = \frac 1 {4\pi\epsilon_0}\...
• 34.3k
1 vote

### Energy lost in a resistor and its temperature

Of course, yes, but if you could raise voltage and keep current constant. But according to Ohm's law, by increasing voltage, current will also rise and this is why the effect of rising voltage doubled....

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