At a distance $d$ from a point charge $Q$, the energy density in its electric field is $u$. If we double the charge, what is the energy density at the same point?

Question

Quizplus · Accepted Answer

The energy density $u$ in the electric field is proportional to the square of the electric field $E$, and $E$ is proportional to the charge $Q$. Therefore, if the charge is doubled, $E$ is doubled, and $u$ increases by a factor of $2^2 = 4$.

At a Distance ddd From a Point Charge QQQ , the Energy Density in Its Electric Field Is

At a Distance $d$ From a Point Charge $Q$ , the Energy Density in Its Electric Field Is