The Resistance in a Wire simulation from PhET shows how a wire’s resistance changes when you move three sliders: resistivity, length and cross-sectional area. The equation on screen resizes as you drag, so you can see the relationship instead of just memorising it. It is free, runs in any browser on a phone, tablet or laptop, and it is a great fit for electricity chapters in Tamil Nadu State Board (Samacheer Kalvi) Science and Physics.
What is the Resistance in a Wire simulation?
This interactive simulation lets you change the resistivity, length and cross-sectional area of a wire and watch how its resistance responds. The wire diagram and the equation update together, with each symbol growing or shrinking as its value changes. Because it runs on HTML5, there is nothing to install, and it works on phones, tablets, Chromebooks and computers.
Middle school to university
Resistivity, length and area sliders
Phone, tablet, Chromebook, PC
English
PhET’s learning goals for this simulation are to predict how changing each variable affects the resistance, and to explain the difference between resistance and resistivity. It also supports maths topics such as inverse relationships and proportional reasoning.
Launch the Resistance in a Wire simulation online
Tap or click inside the player and drag the sliders. Use the full-screen button in the player for a bigger view.
Credit: University of Colorado Boulder
How to use the Resistance in a Wire simulation, step by step
- Predict first. Before touching a slider, say what you think will happen to the resistance.
- Change one slider at a time. Move the length slider and watch the wire stretch and the resistance change.
- Try the area slider. A thicker wire gives the current more room. Notice what happens to the resistance.
- Try the resistivity slider. This changes the material, not the shape of the wire.
- Watch the equation. The letters grow and shrink to show which values are making resistance larger or smaller.
Tip for students: The symbols above the fraction bar make resistance bigger, and the symbol below it makes resistance smaller. The simulation shows this clearly.
The formula behind the simulation: R = ρL/A
R = ρ × L ÷ A
Here R is resistance, ρ (rho) is resistivity, L is the length of the wire and A is its cross-sectional area. Resistance goes up when the wire is longer or the material has higher resistivity, and goes down when the wire is thicker.
Worked example: A copper wire has resistivity 1.7 × 10−8 Ω·m, length 10 m and area 1 mm² (which is 1 × 10−6 m²). Then R = (1.7 × 10−8 × 10) ÷ (1 × 10−6) = 0.17 Ω. Build a similar wire in the simulation and compare the pattern when you double the length.
Resistance key terms explained
These are the words you will meet while using the Resistance in a Wire simulation, with simple meanings.
Resistance (R)
How strongly a wire opposes the flow of electric current. Measured in ohms (Ω).
Resistivity (ρ)
A property of the material itself. Copper has low resistivity; nichrome has high resistivity.
Length (L)
The distance the current must travel through the wire. A longer wire has more resistance.
Cross-sectional area (A)
The size of the wire’s cut end. A thicker wire has less resistance.
Ohm (Ω)
The unit of resistance. One ohm lets one ampere flow for each volt applied.
Ohm’s law
V = I × R. Voltage equals current times resistance.
Direct proportion
When one quantity doubles, the other doubles too. Resistance is directly proportional to length and resistivity.
Inverse proportion
When one quantity doubles, the other halves. Resistance is inversely proportional to area.
Common mistakes: Mixing up resistance (depends on the wire’s shape) with resistivity (depends only on the material), and forgetting that doubling the diameter makes the area four times larger, not twice.
Try the resistance calculator (practice what you explore)
Choose a material, enter the length and area, and see the resistance. Then tap a “what if” button to see how the change affects the result compared with the starting copper wire.
What happens to resistance when you change a variable
| Change | Effect on resistance |
|---|---|
| Length doubled | Resistance doubles |
| Length halved | Resistance halves |
| Area doubled | Resistance halves |
| Resistivity doubled | Resistance doubles |
| Diameter doubled (area ×4) | Resistance becomes one quarter |
Classroom activities for teachers
The Resistance in a Wire simulation fits a single 40-minute period.
- Predict and test (10 min): students write a prediction for each slider, then check it in the simulation.
- Proportion hunt (10 min): find which variables are directly proportional and which are inversely proportional to resistance.
- Design a heater wire (10 min): choose the length, area and material that give a higher resistance, and explain why.
- Exit ticket (10 min): students explain the difference between resistance and resistivity in two sentences.
Looking for the matching chapters? Browse the Science and Physics books on TN SchoolBooks and download the Samacheer Kalvi PDFs, then use this simulation to make the electricity lessons visual. More free science simulations and textbook PDFs are on the home page.
Quick quiz: Test your understanding of resistance
Score: 0 / 5
Resistance in a Wire simulation: frequently asked questions
Is the Resistance in a Wire simulation free?
Yes. PhET simulations are free to run online in a browser. Check PhET’s licensing page for reuse terms.
Does it work on a mobile phone?
Yes. It is built with HTML5 and works on phones, tablets and Chromebooks. Use landscape mode or the player’s full-screen button for a bigger view.
What is the difference between resistance and resistivity?
Resistivity is a property of the material, such as copper or iron. Resistance depends on the material and also on the wire’s length and cross-sectional area.
Why does a thicker wire have less resistance?
A larger cross-sectional area gives the current more paths to flow through, so the resistance is lower. In R = ρL/A, a bigger A makes R smaller.
The Resistance in a Wire simulation turns a formula into something you can drag, test and see. Explore it, take the quiz above, and keep adjusting the sliders until predicting the resistance feels easy.