**Ohm’s law**

*I* = *V* / *R*

**Joule’s law**

*P* = *V · I* = *I*^{ 2} ·* R* = *V*^{ 2} / *R*

**Series circuit rules**

*V*_{T} = *V*_{1} + *V*_{2} + *V*_{3} + …

*I*_{T} = *I*_{1} = *I*_{2} = *I*_{3} = …

*R*_{T} = *R*_{1} + *R*_{2} + *R*_{3} + …

#### 1/*C*_{T} = 1/*C*_{1} + 1/*C*_{2} + 1/*C*_{3} + …

*L*_{T} = *L*_{1} + *L*_{2} + *L*_{3} + …

**Parallel circuit rules**

*V*_{T} = *V*_{1} = *V*_{2} = *V*_{3} = …

*I*_{T} = *I*_{1} + *I*_{2} + *I*_{3} + …

#### 1/*R*_{T} = 1/*R*_{1} + 1/*R*_{2} + 1/*R*_{3} + …

*C*_{T} = *C*_{1} + *C*_{2} + *C*_{3} + …

#### 1/*L*_{T} = 1/*L*_{1} + 1/*L*_{2} + 1/*L*_{3} + …

####
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**Voltage division**

*V*_{1} = *V*_{T} ⋅ *R*_{1} / (*R*_{1}+*R*_{2}+*R*_{3}+…)

_{T}

**Current division**

*I*_{1} = *I*_{T} ⋅ (*R*_{2}+R_{3}+…) / (*R*_{1}+*R*_{2}+*R*_{3}+…)

_{T}

_{2}+R

_{3}+…

**Kirchhoff’s voltage law (KVL)**

#### The sum of voltage drops at a current loop is zero:

#### ∑ *V*_{i} = 0

_{i}

**Kirchhoff’s current law (KCL)**

#### The junction between several circuit elements is called a *node*.

#### The sum of the currents values at a node is zero:

## ∑ *I*_{i} = 0

_{i}

**Capacitance**

*C* = *Q* / *V*

####
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**Parallel plate capacitor**

*C* = ε ⋅ *A* / *l*

#### ε is the permittivity in farad per meter (F/m).

**Permittivity**

#### ε = ε_{} ⋅ ε_{r}

#### ε_{} is the permittivity in the vacuum.

#### ε_{r} is the relative permittivity or dielectric constant.

**Current of capacitor**

*I*_{C}(t) = *C* d*V*_{C}(t) / *dt*

**Voltage of capacitor**

*V*_{C}(t) = *V*_{C}(0)* + *1/*C* ∫* I*_{C}(t)⋅*dt*

_{C}

**Voltage of capacitor**

*V*_{L}(t) = *L* d*I*_{L}(t) / *dt*

####
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**Current of inductor**

*I*_{L}(t) = *I*_{L}(0)* + *1/*L* ∫*V*_{L}(t)⋅*dt*

_{L}

**Energy of capacitor**

*W*_{C} = *C⋅V *^{2} / 2

_{C}

**Energy of inductor**

*W*_{L} = *L⋅I *^{2} / 2

_{L}