Power and energy

• Power:

  • Defined as the rate of energy transferred through a component.
  • $P=$$\frac{E}{T}$ or can be $P=$$VI$
  • As $V=$$IR$ , ($P=$$I\times R\times I$), which equals $P=$$I^2R$
  • From $I=$$\frac{V}{R}$, $P=$$V\times\frac{V}{R}$ : which equals $P=$$\frac{V^2}{R}$
• Kilowatt-hours:

  • 1kWh is the energy transferred by a device with a power of 1kw in one hour
  • 1kWh= 1000W$\times$(60$\times$60) = 3,600,000J
  • kWh->J= $\times3.6\times10^6$
  • J->kWh= $\div3.6\times10^6$
• Electron-volt:

  • 1eV is the work done when one electron is accelerated by a potential difference of 1V
  • $E=$$QV$
  • 1eV=$1.6\times10^{-19}\times1v$ = $1.6\times10^{-19}$
  • eV->J= $\times1.6\times10^{-19}$
  • J->eV= $\div1.6\times10^{-19}$