Drift velocity and charging a capacitor.

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SUMMARY

The discussion centers on the relationship between drift velocity and the charging time of a capacitor in electrical circuits. It is established that the charging time, denoted by the time constant \(\tau\), can be derived from the drift velocity of electrons in the conductor. Participants clarified that while the drift velocity is slow, the large number of electrons in the conductor contributes significantly to the charging process. The conversation also addressed misconceptions about electron movement in wires and the role of excess charges in diodes.

PREREQUISITES
  • Understanding of drift velocity in conductors
  • Familiarity with capacitive circuits and time constants
  • Basic knowledge of electron behavior in metals
  • Concept of Coulomb forces and charge distribution
NEXT STEPS
  • Study the derivation of the time constant \(\tau\) in RC circuits
  • Learn about the relationship between drift velocity and current density
  • Explore the concept of charge distribution in semiconductor diodes
  • Investigate the effects of temperature on drift velocity and capacitance
USEFUL FOR

Electrical engineers, physics students, and anyone interested in understanding the dynamics of capacitors and electron behavior in conductive materials.

jhammin
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I'm having trouble understanding where the charging time in a capacitor actually comes from. Is it possible to derive the \tau of a capacitive circuit from the drift velocity of the electrons? Are charges literally moving from the conductors onto the metal plates of the capacitor?
 
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Yes, the drift velocity is quite slow but there are a lot of electrons in the "electron gas" of the metal conductor.
 
The charging time of capacitor depends on its energy absorption, which can be used directly to get the drift velocity. Looks like I answered my own question.

I was caught up in the notion that electrons never actually enter or leave a wire. I'm not sure how i reached that idea because obviously the dispersion region in a diode depends on how many excess charges are available to be shared across the junction.
 
drummin said:
Yes, the drift velocity is quite slow but there are a lot of electrons in the "electron gas" of the metal conductor.

Ya, I was thrown off by the shear number of electrons. I was also thinking too much about the individual Coulomb forces between each electron.
 

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