How fast do electrons really move in a wire?
"How fast do electrons really move in a wire?" is a free, interactive Class 12 Physics simulation for NEET and JEE, built on the lesson "Electron drift and where resistivity comes from" in Current Electricity. This copper wire narrows in the middle. Press Switch on. The blue dots are free electrons; they drift against the current, from right to left. Compare how fast they move in the thick and thin parts. The current is the same through every cross-section; the drift speed, fractions of a mm/s, is larger where the wire is thinner, since v_d = I/(neA). A lamp lights at once because the field, not the electrons, travels fast. JEE Main asked 65 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
From the lesson Electron drift and where resistivity comes from 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 § "Drift of Electrons and the Origin of Resistivity"
- Free electrons collide frequently with the ions of the lattice. The average time between successive collisions is the relaxation time τ.
- An applied field E gives each electron an acceleration −eE/m between collisions, producing a small average velocity opposite to E, the drift velocity v_d = −eEτ/m.
- The current through a conductor of area A with n free electrons per unit volume is I = neAv_d.
- Drift speeds are very small, typically a fraction of a millimetre to a few millimetres per second, while the random thermal speeds of electrons are very large.
- A lamp lights almost at once when switched on because the electric field is set up along the whole wire nearly instantly, starting all the electrons drifting together; it is not because electrons rush from the switch.
- Combining the two results gives the resistivity in terms of microscopic quantities: ρ = m/(ne²τ).
- For a wire of non-uniform cross-section carrying a steady current, the current is the same at every section, so the drift speed is larger where the wire is thinner.
Questions
3 answers
- What does the "How fast do electrons really move in a wire?" simulation show?
- This copper wire narrows in the middle. Press Switch on. The blue dots are free electrons; they drift against the current, from right to left. Compare how fast they move in the thick and thin parts.
- 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 "Electron drift and where resistivity comes from" in Current Electricity (Class 12 Physics).
Embed this simulation
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Teaching this idea? Put the simulation on your own page or LMS with this code.