---
title: "Resistance in Series and Parallel"
description: "Resistances in series add, while adding a parallel branch lowers the total resistance and raises the current drawn from the supply. Each rule is checked against measurements rather than taken on trust"
canonical: https://lightmysky.com/learn/science/resistance-in-series-and-parallel-mt_B29m3h5B75
source: https://lightmysky.com/learn/science/resistance-in-series-and-parallel-mt_B29m3h5B75.md
retrieved: 2026-09-12
---

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# Resistance in Series and Parallel

Resistances in series add, while adding a parallel branch lowers the total resistance and raises the current drawn from the supply. Each rule is checked against measurements rather than taken on trust.

Subject: Science · Area: Energy · Ages 14 to 16
Page: https://lightmysky.com/learn/science/resistance-in-series-and-parallel-mt_B29m3h5B75

## Ready when they can

- Calculates the total resistance of resistors in series and predicts the current
- Explains why two identical resistors in parallel halve the total resistance
- Predicts what happens to supply current when a lamp is added in parallel, and checks it in a circuit

## Lesson: One path or many paths

Resistors in series share one path, so the same current flows through each of them. Their resistances simply add: two 10 ohm resistors in series act like one 20 ohm resistor. The supply voltage splits across them in proportion to each resistance.

Resistors in parallel offer extra paths, so the total always falls below the smallest branch. Two identical resistors in parallel halve the total. Each branch feels the full supply voltage, and the supply current rises because charge has more routes at once.

**Example.** House wiring uses parallel so every socket sees full voltage and one appliance never starves the rest. An old string of lights in series dies together when one bulb fails. Predict each current before you measure, then check with meters.

**Tip.** Each meter has a correct home. An ammeter goes in series because it must carry the current, and a voltmeter goes across the component because it measures the push between two points. Adding a lamp in parallel always lowers total resistance and raises supply current.

**Recap.** Series adds resistance on one path, while parallel adds paths and lowers it.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Current-Voltage Graphs for Components](https://lightmysky.com/learn/science/current-voltage-graphs-for-components-mt_n_CiOa-05J)

## Opens up

- [Electrical Power and the Cost of Running Appliances](https://lightmysky.com/learn/science/electrical-power-and-the-cost-of-running-appliances-mt_099G0drIbk)
- [Discharging a Capacitor and the Time Constant](https://lightmysky.com/learn/science/discharging-a-capacitor-and-the-time-constant-mt_5sjDPudyad)
- [Resistivity and What Sets a Wire's Resistance](https://lightmysky.com/learn/science/resistivity-and-what-sets-a-wires-resistance-mt_A4f8THP-xm)
- [Thermistors, Light-Dependent Resistors and Sensing Circuits](https://lightmysky.com/learn/science/thermistors-light-dependent-resistors-and-sensing-circuits-mt_d92v1CiqIG)