The Variable Resistor

Part of the Electricity and Magnetism section of Coddy's Physics journey. Lesson 27 of 51.

A variable resistor can be turned up or down.

A circuit with a variable resistor

R up: the current drops and the terminal voltage rises. R down: the current grows and the terminal voltage falls.

The power reaching R is largest when

$R = r$

the outside resistance equals the internal one.

Challenge

A battery with EMF $12\ \mathrm{V}$ and internal resistance $2\ \mathrm{\Omega }$ drives a current through a variable resistor set to $2\ \mathrm{\Omega }$ . How much power $P$ reaches the variable resistor?

Try it yourself

Solve for $P$

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Electricity and Magnetism

1Electric Charge and Force

Electric Charge Coulomb's Law Several Charges Recap - Charges in a Line

4Charged Conductors

The Charged Sphere Connecting Spheres Recap - Beam Between Plates

7Real Batteries

Internal ResistanceThe Variable ResistorAmmeters and Voltmeters Recap - Flashlight

10Magnetic Fields

Magnets and Magnetic Fields Field of a Wire Loops and Solenoids Recap - Electromagnet

2The Electric Field

The Electric Field Field of Several Charges The Uniform Field A Charge in a Uniform Field Recap - Stopping a Proton

5Capacitors

The Capacitor Combining Capacitors Changing a Capacitor Recap - Camera Flash

8Kirchhoff's Laws

The Junction Rule The Loop Rule Solving Two Loops Recap - Charging a Battery

11Magnetic Forces

Force on a Moving Charge Circles in a Field Force on a Wire Two Parallel Wires Recap - Current Balance

3Energy and Potential

Electric Potential Energy Electric Potential Field and Potential Recap - Accelerating Ions

6Current and Resistance

Current and Voltage Resistance and Ohm's Law Series and Parallel Electric Power Recap - Fairy Lights

9Capacitors in Circuits

A Capacitor in a Circuit Charging a Capacitor Discharging a Capacitor Recap - Defibrillator

12Induction

A Rod Moving in a Field Magnetic Flux Faraday's Law Lenz's Law Recap - Generator