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- PHY102 Physics II © Dr.Cem Özdoğan
- 26-6 A Microscopiv view of Ohm’s Law
- It is often assumed that the conduction electrons in a metal move with a single effective speed veff, and this speed is essentially independent of the temperature.
- For copper, veff =1.6 x106 m/s.
- When we apply an electric field to a metal sample, the electrons modify their random motions slightly and drift very slowly with an average drift speed vd.
- The drift speed in a typical metallic conductor is about 5 x10-7 m/s, less than the effective speed (1.6 x106 m/s) by many orders of magnitude.
- The motion of conduction electrons in an electric field is a combination of the motion due to random collisions and that due to E.
- If an electron of mass m is placed in an electric field of magnitude E, the electron will experience an acceleration:
- In the average time τ between collisions, the average electron will acquire a drift speed of vd =aτ.