Resistance in a Wire (R = ρL/A)
Change a wire's length, thickness and material and watch electrons collide and the resistance change.
Drag the right end of the wire to make it longer and the round handle to make it thicker. Choose a material. Long, thin wires resist more.
About the Resistance in a Wire (R = ρL/A)
Free resistance in a wire (r = ρl/a). Change a wire's length, thickness and material and watch electrons collide and the resistance change. Drag, change the sliders and see the result live. No sign-up, works on phone and computer. Built for physics, the resistance in a wire (r = ρl/a) runs instantly in your browser: change a setting or drag an object and the result updates at once, so you learn by trying things out rather than only reading about them.
Change a wire's length, thickness and material and watch electrons collide and the resistance change. Use it to explore physics ideas at your own pace, then check what you found against the key ideas further down this page.
How to use the Resistance in a Wire (R = ρL/A)
- Use the controls to change Material, Length, Thickness (area). The simulation reacts instantly.
- Pick an option such as Copper, Aluminium, Iron, Nichrome to switch modes or load an example.
- Where you see a glowing handle, object, weight or atom, drag it with your mouse or finger. Everything responds in real time.
- Watch the readouts and graphs update as you experiment, and compare what you see with the key ideas below.
Things to try
- Double the length and read the resistance.
- Compare copper and nichrome.
- Make the wire as thick as possible.
Key ideas you can learn
- R = ρ L / A.
- A longer wire has more resistance.
- A thicker wire has less resistance.
- Materials have different resistivity ρ.
Where this is used in the real world
Power cables are thick copper to reduce loss; heater elements are thin nichrome to make heat.
Who is this simulation for?
Physics students in middle school, high school and first-year university, teachers who want a quick demonstration for the projector, and anyone revising for exams. It works well for flipped classrooms because students can explore before the lesson.
For teachers: project it on the board, let students predict what will happen, then run it together. For students: change one thing at a time and write down what changes.
Frequently asked questions
Why does a thin wire have higher resistance?
There is less space for electrons to flow, so they collide with atoms more.
What is resistivity?
A property of a material that says how strongly it resists current, measured in ohm-metres.
Is the Resistance in a Wire (R = ρL/A) free to use?
Yes. It is completely free, with no signup, no download and no ads inside the simulation. It runs in your web browser.
Does the Resistance in a Wire (R = ρL/A) work on a phone or tablet?
Yes. It uses touch as well as the mouse, so you can drag objects with your finger. A larger screen makes the controls easier to see.