Current Electricity
Class 12 · Current Electricity
Drift Velocity
v_d = I/(nAe). Animated electrons with thermal motion + tiny drift.
Key Notes
01
Current = nAev_d — electrons move with average drift velocity v_d (typically mm/s).
02
Despite v_d being slow, signals propagate near speed of light because the EM field travels fast.
03
n (charge density), A (cross-section), e (electron charge) all enter linearly.
Formulas
Drift velocity
Microscopic origin of current.
Important Points
For Cu: n ≈ 8.5 × 10²⁸/m³.
Mobility μ = v_d/E. σ = neμ.
Drift Velocity 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.