Stretch a wire and watch its resistance
"Stretch a wire and watch its resistance" is a free, interactive Class 12 Physics simulation for NEET and JEE, built on the lesson "Electric currents in conductors and Ohm's law" in Current Electricity. Move the slider. The orange wire is the grey one pulled out to n times its length. Its volume stays the same, so it gets thinner as it gets longer. Watch R and the graph. Stretching changes both l and A, so at constant volume R ∝ l² (and R ∝ 1/d⁴). A longer piece of the same wire only has R ∝ l. Resistivity does not change at all: it belongs to the material, not the shape. JEE Main asked 65 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
From the lesson Electric currents in conductors and Ohm's law in Current Electricity. Change the values and watch what happens.
In JEE Main
42 shifts analysed
65 questions from Current Electricity across the 42 JEE Main shifts Lumi has analysed (2017–2026).
The idea behind it
NCERT § "Ohm's Law"
- In metals the charge carriers are free electrons; in electrolytes both positive and negative ions carry current.
- Without an applied field, free electrons move randomly in all directions and there is no net flow; a steady current needs a steady electric field maintained by a source such as a cell.
- Ohm's law: the current through a conductor is proportional to the potential difference across it, V = IR, where R is its resistance (unit ohm, Ω).
- Resistance depends on the dimensions of the conductor: R = ρl/A, directly proportional to length and inversely to area of cross-section.
- Resistivity ρ depends on the material and the temperature, not on the size or shape; its SI unit is Ω m.
- Current density j is current per unit area normal to the flow (unit A m⁻²); Ohm's law in vector form is j = σE, where σ = 1/ρ is the conductivity.
- When a wire of fixed volume is stretched to n times its length, its area becomes 1/n times, so its resistance becomes n² times.
Questions
3 answers
- What does the "Stretch a wire and watch its resistance" simulation show?
- Move the slider. The orange wire is the grey one pulled out to n times its length. Its volume stays the same, so it gets thinner as it gets longer. Watch R and the graph.
- Does JEE Main ask questions from Current Electricity?
- Yes. JEE Main asked 65 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
- Is this simulation free?
- Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "Electric currents in conductors and Ohm's law" in Current Electricity (Class 12 Physics).
Embed this simulation
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