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- PHY102 Physics II © Dr.Cem Özdoğan
- 26-3 Current Density, Drift Speed
- In the figure, the drift of positive charge carriers is in the direction of the applied electric field, E. If we assume that
- these charge carriers all move with the same drift speed vd,
- the current density J is uniform across the wire’s cross-sectional area A,
- The number of charge carriers in a length L of the wire is nAL. Here n is the number of carriers per unit volume (Carrier charge density, C/m3).
- The total charge of the carriers in the length L, each with charge e, is then
- The total charge moves through any cross section of the wire in the time interval
- When a conductor has a current passing through it, the electrons move randomly, but they tend to drift with a drift speed vd in the direction opposite that of the applied electric field that causes the current.
- The drift speed is tiny compared with the speeds in the random motion.
- Drift speed: vd :Velocity at which electrons move in order to establish a current.