---
title: "Current-Voltage Graphs for Components"
description: "Measuring current against potential difference for a fixed resistor, a filament lamp and a diode, then reading each graph's shape. A straight line means constant resistance, and a bend means the resis"
canonical: https://lightmysky.com/learn/science/current-voltage-graphs-for-components-mt_n_CiOa-05J
source: https://lightmysky.com/learn/science/current-voltage-graphs-for-components-mt_n_CiOa-05J.md
retrieved: 2026-09-12
---

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# Current-Voltage Graphs for Components

Measuring current against potential difference for a fixed resistor, a filament lamp and a diode, then reading each graph's shape. A straight line means constant resistance, and a bend means the resistance is changing.

Subject: Science · Area: Energy · Ages 14 to 15
Page: https://lightmysky.com/learn/science/current-voltage-graphs-for-components-mt_n_CiOa-05J

## Ready when they can

- Builds a test circuit with an ammeter in series and a voltmeter across the component
- Plots current against potential difference for both directions and describes the shape
- Explains the lamp's curve by its filament heating up, and the diode's shape by current in one direction only

## Lesson: Reading current against voltage

To test a component you build a circuit with the ammeter in series and the voltmeter across the component. Change the supply step by step and record each current with its voltage. Those pairs become the dots of your current against voltage graph.

A fixed resistor gives a straight line through zero, because current rises in step with voltage. The steepness of the line is set by the resistance. A steep line means low resistance, since more current flows for each volt.

**Example.** A filament lamp starts like a resistor, then its graph bends flat at higher voltages. The filament heats up, its resistance climbs, and current rises more slowly. A diode is stricter: it passes current one way and blocks it the other, so its graph stays near zero on the reverse side and climbs fast on the forward side.

**Tip.** Reverse the supply and the resistor and lamp graphs mirror through zero. The diode keeps its flat side on reverse, which is how you spot it. A lopsided graph means a diode, not a resistor or a lamp.

**Recap.** Straight means steady resistance, a bend means heating, and lopsided means a diode.

## Practice

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

## Needs first

- [Ohm's Law: voltage, current, resistance](https://lightmysky.com/learn/science/ohms-law-voltage-current-resistance-mt_H3ZDK0EYNV)
- [Series vs parallel circuits](https://lightmysky.com/learn/science/series-vs-parallel-circuits-mt_loEMaQ8kFA)

## Opens up

- [Resistivity and What Sets a Wire's Resistance](https://lightmysky.com/learn/science/resistivity-and-what-sets-a-wires-resistance-mt_A4f8THP-xm)
- [Resistance in Series and Parallel](https://lightmysky.com/learn/science/resistance-in-series-and-parallel-mt_B29m3h5B75)
- [Thermistors, Light-Dependent Resistors and Sensing Circuits](https://lightmysky.com/learn/science/thermistors-light-dependent-resistors-and-sensing-circuits-mt_d92v1CiqIG)