Series vs. parallel

Series connections #

Things that are connected in series are connected end-to-end, like a train.

If you connect a bunch of resistors in series, the resistances add up. All the current has to flow through every resistor, so each resistor restricts the flow more.

resistors in series

Above, you see 3 resistors, R1, R2, and R3, connected in series.

If each resistor had a resistance of 1k, and the battery above supplied 6 V to the resistors, how much current would flow?

See the answer ...

Hey, 2 mA is right! If each resistor had a resistance of 1k, the total resistance of the three in series would be 3k. Our old friend, Ohm’s law, tells us that

\(V / R = I\) , and \(6 / 3000 = 0.002\) .

Parallel connections #

Things that are connected in parallel are connected such that they share a common input as well as a common output.

If you connect a bunch of resistors in parallel, the total resistance decreases as you add more resistors. If you connect, say, 5 identical resistors in parallel, the total resistance will be 1/5th of a single resistor. The current will split into 5 separate streams, each equal to 1/5th of the total current.

resistors in parallel

Above, you see two resistors, R1 and R2, connected in parallel.

If, as above, each resistor had a resistance of 1k, and the battery above supplied 6 V to the resistors, how much current would flow?

See the answer ...

Hey, 12 mA is right! If each resistor had a resistance of 1k, the total resistance of the two in parallel would be 500 ohms. Ohm’s law tells us that (V / R = I) , and (6 / 500 = 0.012) .