Adding resistors in a circuit can be done in two ways: in series or in parallel. The method you choose will affect the total resistance of the circuit.

## How to Add Resistors in Series

Adding resistors in series is quite straightforward. When resistors are connected in series, the current through each resistor is the same and the total resistance is the sum of the resistances of each resistor.

Here’s how you can calculate the total resistance for resistors in series:

**Step 1: Identify the Resistors**

First, you need to identify all the resistors that are connected in series in your circuit.

**Step 2: Note the Resistance Values**

Next, note down the resistance value of each resistor. You can usually find this marked on the resistor itself or you can measure it with a multimeter. The unit of resistance is ohms (Ω).

**Step 3: Add the Resistance Values**

To find the total resistance, simply add up the resistance values of all the resistors.

R_total = R1 + R2 + R3 + … + Rn

For example, if you have three resistors in series with resistances of 2 ohms, 3 ohms, and 5 ohms respectively, the total resistance would be 2 + 3 + 5 = 10 ohms.

This total resistance is what the power source “sees” when looking into the circuit.

## How to Add Resistors in Parallel

Adding resistors in parallel involves a different calculation compared to adding them in series. When resistors are connected in parallel, the voltage across each resistor is the same, but the currents through them may be different. The total resistance of the circuit decreases as you add more resistors in parallel.

Here’s how you can calculate the total resistance for resistors in parallel:

**Step 1: Identify the Resistors**

First, identify all the resistors that are connected in parallel in your circuit.

**Step 2: Note the Resistance Values**

Next, note down the resistance value of each resistor. You can usually find this marked on the resistor itself or you can measure it with a multimeter. The unit of resistance is ohms (Ω).

**Step 3: Calculate the Reciprocal of Each Resistance**

For each resistor, calculate the reciprocal of its resistance (1/R).

**Step 4: Add the Reciprocals**

Add together all the reciprocals from step 3.

**Step 5: Take the Reciprocal of the Result**

Finally, take the reciprocal of the result from step 4. This gives you the total resistance of the resistors in parallel.

So the formula is:

1 / R_total = 1 / R1 + 1 / R2 + 1 / R3 + … + 1 / Rn

For example, if you have two resistors in parallel, one with a resistance of 4 ohms and the other with a resistance of 6 ohms, the total resistance would be 1 / ((1/4) + (1/6)) ≈ 2.4 ohms.

## Conclusion

Understanding how to add resistors, whether in series or parallel, is crucial for designing and understanding electronic circuits. It allows you to control the current flow and voltage drop in various parts of the circuit.