Current Electricity
Class 12 · Current Electricity

Microscopic Current (Drude)

σ = ne²τ/m. See ions + electrons + collisions on atomic scale.

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Key Notes

01

Drude model: free electrons accelerate in E, scatter off ions every τ seconds.

02

Average drift v_d = eEτ/m. Conductivity σ = ne²τ/m.

03

Resistivity ρ = 1/σ. Increases with T because τ shortens.

Formulas

Drude conductivity

Microscopic origin.

Drift velocity

Linear in E.

Important Points

τ for Cu at room T ≈ 2.5 × 10⁻¹⁴ s — extremely short.

Mean free path ℓ = v_F·τ where v_F is Fermi velocity (not v_d).

Microscopic Current (Drude) notes from sciphylab (also known as SciPhy, SciPhy Lab, SciPhy Labs, Physics Lab). Class 12 physics revision for JEE Mains, JEE Advanced, NEET UG, AP Physics 1/2/C, SAT, and CUET-UG.