Imagine the circulatory system again. There are instances where blood vessels split into multiple smaller vessels and, at other times, combine together. Similarly, in a circuit, resistors can be arranged in series or in parallel, each having its unique characteristics.

**Series Resistors: A Single Pathway**

When resistors are in series, it’s akin to a succession of multiple plaque filled vessels placed one after the other, each causing there own blood slow down. There’s only one pathway for the current, much like there’s one route for the blood.

Just as the total resistance of multiple plaque filled vessels in series would be the sum of their individual resistances, the combined resistance of series resistors is the sum of each resistor’s resistance: \[ R_{total} = R_1 + R_2 + R_3 + … \]

**Quick Tip: **

If you’re asked to find the total resistance of several resistors connected in series, immediately disregard any answer choices that show a resistance equal to or lower than the highest individual resistor’s value. In a series circuit, the total resistance is the sum of all individual resistances, so it will always be greater than the resistance of the single highest resistor.

**Parallel Resistors: Alternate Pathways in Times of Blockage**

Imagine an artery branching off into multiple arterioles. In the event of a blockage in one arteriole, blood can still flow through the remaining pathways. This is the very essence of parallel resistors. When there’s resistance or even a “blockage” in one pathway, electrons can divert through the other paths, ensuring the current remains uninterrupted.

The combined resistance in parallel resistors is reminiscent of the circulatory advantage of having multiple arterioles branching from an artery. With more pathways, blood flow encounters less resistance overall, ensuring efficient distribution to all areas.

In circuits, when resistors are parallel, they provide multiple routes for the current, spreading out electron flow and effectively reducing the overall resistance. This is expressed mathematically as: \[ \frac{1}{R_{total}} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} + … \]

**Quick Tip:** When calculating the total resistance of resistors in parallel, look for the answer that is less than the smallest individual resistor’s resistance. In a parallel configuration, the total resistance decreases because the electrical current has multiple paths to take. Therefore, the overall resistance will always be lower than the resistance of the smallest resistor in the group.

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