Simulation · Physics · Class 12

Stretch a wire and watch its resistance

From the lesson Electric currents in conductors and Ohm's law in Current Electricity. Change the values and watch what happens.

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.

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