Menu

Resistance and Ohm's Law

Part of the Electricity and Magnetism section of Coddy's Physics journey. Lesson 22 of 51.

Ohm's law: the current through a resistor is proportional to the voltage across it:

$V = IR$

with R in ohms ( $1\ \mathrm{\Omega }$ = $1\ \mathrm{V/A}$ ).

A battery and a resistor

A wire's resistance:

$R = \rho\,\frac{L}{A}$

Longer: more resistance; thicker: less. ρ, the resistivity, belongs to the material.

Challenge

A copper wire is $10\ \mathrm{m}$ long with a cross-section of $1\ \mathrm{mm^2}$ ( $1\times10^{-6}\ \mathrm{m²}$ ). Copper's resistivity is $1.7\times10^{-8}\ \mathrm{Ω·m}$ . What current $I$ flows when $1.7\ \mathrm{V}$ is put across the wire? Work out its resistance first.

Try it yourself

Physics diagram: circuit

Solve for $I$

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 Resistance The Variable Resistor Ammeters 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 VoltageResistance and Ohm's LawSeries 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