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Microscopic View of Current quiz #1 Flashcards

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Microscopic View of Current quiz #1
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  • Which type of material best carries electric current according to the microscopic view of current?
    A conductor best carries electric current because it has a high density of free electrons that are able to move through the material, allowing for efficient current flow.
  • What is the physical meaning of the mean free time (tau) for electrons in a conductor?
    The mean free time is the average time an electron travels between collisions with atoms in the conductor. It determines how frequently electrons are scattered as they move under the influence of an electric field.
  • How does the drift velocity of electrons in a conductor compare to their speed in a vacuum?
    The drift velocity in a conductor is much slower than in a vacuum because electrons frequently collide with atoms. These collisions impede their motion and reduce their average speed.
  • How is the free electron density in a conductor determined from the total electron density?
    The free electron density is found by multiplying the total electron density by the fraction of electrons that are free to move. For example, if 1% of electrons are free, the free electron density is 1% of the total.
  • What is the relationship between resistivity and conductivity in a material?
    Resistivity and conductivity are inverses of each other. High resistivity means low conductivity and vice versa.
  • Which physical constants are needed to calculate the drift velocity of electrons in a conductor?
    To calculate drift velocity, you need the electron charge, the electric field, the electron mass, and the mean free time. These values are combined in the drift velocity formula.
  • How does increasing the mean free time affect the conductivity of a material?
    Increasing the mean free time increases the conductivity because electrons can travel longer without scattering. This allows more efficient current flow through the material.
  • What is the formula for current density in terms of free electron density, electron charge, mean free time, electron mass, and electric field?
    The formula for current density is n e squared tau over m times the electric field. Here, n is the free electron density, e is the electron charge, tau is the mean free time, and m is the electron mass.
  • If a conductor has a total electron density of 1 x 10^20 electrons/m^3 and 1% are free, what is the free electron density?
    The free electron density is 1 x 10^18 electrons/m^3. This is calculated by taking 1% of the total electron density.
  • How can you solve for the mean free time if you know the conductivity, free electron density, and electron charge?
    You solve for the mean free time by rearranging the conductivity formula: tau equals the electron mass times conductivity divided by free electron density times electron charge squared. This allows you to calculate tau directly from the given values.