Electrical theorems are essential tools that allow us to analyze and solve electrical circuits more effectively. When working with circuits, especially those that have multiple voltage sources and resistances, it can be confusing to understand how they interact with each other.

These electrical theorems provide us with strategies to simplify these circuits and make calculations easier.

## Superposition Theorem

We start with the Superposition theorem, which is one of the most used in linear circuits.

This electrical theorem states that in a circuit with more than one voltage or current source, the total effect on a load can be determined by adding the effects of each source individually. This means that you can “turn off” the other sources while analyzing only one.

Imagine you have a circuit with two voltage sources. To calculate the current through a resistor, you must first determine the effect of the first source, then that of the second. By calculating both effects separately and adding them together, you get the total current in the resistor.

## Thévenin's theorem

Another key theorem is Thévenin's Theorem. This theorem tells us that any linear circuit can be simplified to an equivalent circuit consisting of a single voltage source and a series resistor.

The voltage source is called the Thévenin voltage and the resistance is the Thévenin resistor.

To apply Thévenin's Theorem, you must first:

- Identify the terminals of the circuit you want to analyze.
- Calculate the voltage between those terminals when no load is connected (this gives you the Thévenin voltage).
- Find the equivalent resistance seen from those terminals, turning off all sources (short circuits for voltage sources and open circuits for current sources).
- Once you have these values, you can replace the original circuit with the Thévenin source and its resistor to simplify your calculations.

## Norton's theorem

Norton's Theorem is complementary to Thévenin's Theorem. This theorem states that any linear circuit can be represented by a current source in parallel with a resistance. This source is called the Norton current, and the resistance is the Norton resistance.

### Comparison with Thévenin's theorem

The main difference between these two theorems is that Thévenin's theorem uses a series voltage source, while Norton's theorem uses a parallel current source.

However, both theorems are equivalent and you can convert one into the other using the appropriate relations. This means that, depending on the situation, you can choose the theorem that is easier for you to apply.

## Maximum power transfer theorem

The maximum power transfer theorem tells us that to maximize the power transferred to a load, the load resistance must be equal to the output resistance of the circuit. This theorem is fundamental in applications where maximizing power delivery is crucial, such as in audio systems and communications.

### Highlighted implications

This theorem has important practical implications.

In situations where this condition is not met, the load may not receive the maximum power it could. This can result in poor circuit performance.

Therefore, in circuit design, it is critical to consider load resistance to ensure that power transfer is maximized.

## Millman's theorem

Millman's Theorem is used to analyze circuits that have multiple voltage sources and resistors connected in parallel.

This theorem allows the voltage at a common node to be calculated from the voltages and resistances of the sources connected to that node.

The application of Millman's Theorem is quite simple. When calculating the voltage at the common node, the voltage of each source and the associated resistance are considered.

## Tellegen's theorem

Tellegen's Theorem is a conservation of energy principle that applies to any electrical circuit. This theorem states that the sum of the instantaneous power in a circuit is equal to zero. That is, the power entering a node is equal to the power leaving it.

This theorem reinforces the idea that energy is neither created nor destroyed; it simply transforms.

## Power theorem

Finally, the Power Theorem states that the power dissipated in a resistor is equal to the product of the square of the current multiplied by the resistance.

To calculate the power in a resistor, you can use the formula P=I ^{2} R. This means that if you know the current flowing through the resistor and its value, you can determine how much power is dissipated.