## How to calculate the resistance of a system of resistors connected in series and parallel?

Calculating the total resistance in circuits with resistors connected in series and parallel requires understanding how these configurations affect the flow of current and voltage across the resistors. Here’s how to calculate the resistance in both setups:

### Resistors in Series

When resistors are connected in series, the current flowing through each resistor is the same, but the voltage across each resistor can be different. The total resistance ((R_{total})) of the series circuit is the sum of all individual resistances.

For (n) resistors connected in series, the total resistance is given by:

[R_{total} = R_1 + R_2 + R_3 + \ldots + R_n]

**Example**: If you have three resistors in series with resistances of 2 Ω, 3 Ω, and 5 Ω, the total resistance is (2 Ω + 3 Ω + 5 Ω = 10 Ω).

### Resistors in Parallel

In a parallel connection, all resistors are directly connected to the voltage source, so each resistor experiences the same voltage, but the current through each resistor can be different. The total resistance of a parallel circuit is found by taking the reciprocal of the sum of the reciprocals of each individual resistance.

For (n) resistors connected in parallel, the total resistance ((R_{total})) is given by:

[\frac{1}{R_{total}} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} + \ldots + \frac{1}{R_n}]

To find (R_{total}), you take the reciprocal of the sum:

[R_{total} = \frac{1}{\left(\frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} + \ldots + \frac{1}{R_n}\right)}]

**Example**: If you have three resistors in parallel with resistances of 2 Ω, 3 Ω, and 6 Ω, you first calculate the reciprocal of each resistance and add them:

[\frac{1}{R_{total}} = \frac{1}{2} + \frac{1}{3} + \frac{1}{6} = \frac{3}{6} + \frac{2}{6} + \frac{1}{6} = \frac{6}{6} = 1]

Then take the reciprocal of the sum to find the total resistance:

[R_{total} = \frac{1}{1} = 1 Ω]

### Key Differences

**Series**: The total resistance increases with each added resistor because the current has to pass through each resistor sequentially, facing more opposition.
**Parallel**: The total resistance decreases as more paths for the current are created with each added resistor, making it easier for the current to flow.

Understanding these principles allows for effective circuit design and analysis in both theoretical and practical applications in electronics and electrical engineering.