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Key Equations
# Key Equations

electric current I is the charge $\Delta Q$ that passes a plane per unit time $\Delta t$ |
$I=\frac{\Delta Q}{\Delta t}$ |

an ampere is the coulombs per unit time that pass a plane |
$1\text{\hspace{0.17em}}\text{A}=1\text{\hspace{0.17em}}\text{C/s}$ |

Ohm’s law: the current I is proportional to the voltage V, with the resistance R being the constant of proportionality |
$V=IR$ |

the equivalent resistance of N resistors connected in series |
${R}_{\text{equiv}}={R}_{1}+{R}_{2}+\cdots +{R}_{N}$ |

the equivalent resistance of N resistors connected in parallel |
${R}_{\text{equiv}}=\frac{1}{1/{R}_{1}+1/{R}_{2}+\cdots +1/{R}_{N}}$ |

for a given current I flowing through a potential difference V, the electric power dissipated |
$P=IV$ |

for a given current I flowing through a resistance R, the electric power dissipated |
$P={I}^{2}R$ |

for a given voltage difference V across a resistor R, the electric power dissipated |
$P=\frac{{V}^{2}}{R}$ |