Key Equations

electric current I is the charge $Δ Q$ that passes a plane per unit time $Δ t$	$I = \frac{Δ Q}{Δ t}$
an ampere is the coulombs per unit time that pass a plane	$1 A = 1 C/s$
Ohm’s law: the current I is proportional to the voltage V, with the resistance R being the constant of proportionality	$V = I R$

the equivalent resistance of N resistors connected in series

R_{equiv} = R_{1} + R_{2} + \dots + R_{N}

the equivalent resistance of N resistors connected in parallel

R_{equiv} = \frac{1}{1 / R_{1} + 1 / R_{2} + \dots + 1 / R_{N}}

for a given current I flowing through a potential difference V, the electric power dissipated	$P = I V$
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	$P = \frac{V^{2}}{R}$

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