Energy

Electric potential energy

$U_E=k\frac{q_1{q}_2}{r}$

• Electric potential energy is the energy stored in a system of charges due to their positions relative to each other
• The work done in bringing a charge from infinity to that point

Electric energy

• Electric energy is the capacity to do work
• $E={\int }_{t_0}^{t}Pdt={\int }_{t_0}^{t}VIdt$
  • $E$ is electrical energy (in joules) absorbed or supplied by an element from time $t_0$ to time $t$
  • $P$ is power (in watts)
  • $V$ is voltage (in volts)
  • $I$ is current (in amperes)
• Units of electrical energy
  • $1\mathsf{J}=1\mathsf{C}\cdot \mathsf{V}$ (joule)
  • $1\mathsf{kWh}=3.6\times 10^6\mathsf{J}$ (kilowatt-hour) which is the energy consumed by a 1-kilowatt appliance in 1 hour
  • $1\mathsf{eV}=1.6\times 10^{-19}\mathsf{J}$ (electronvolt) which is the energy acquired by a particle carrying a charge whose magnitude equals that on the electron as a result of moving through a potential difference of $1\mathsf{V}$