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Lecture

# January 24.doc

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School
Department
Physics
Course
PHYS 102
Professor
Zaven Altounian
Semester
Winter

Description
Phys 102 Alanna Houston January 24, 2008 DIRECT ELECTRIC CURRENT Conductors / Metals: - In metals, the valence electrons are very weakly attached to their parent atoms - These electrons can be considered to be “free” - If an electric field is applied, the free electrons will move in the direction of the force applied on them. - - The electric current is the rate of flow of charge across a surface - - The direction of the electric current is defined as the direction of movement of a positive charge Electron Drift Velocity: - Electrons have thermal energy. For free electrons, this energy is transformed into kinetic energy. Typically, the free electrons acquire speeds of the order of 10^6 m/s. - But the directions of the velocities are random i.e. no net movement of the charges - When an electric field is applied, the free electrons move in a direction opposite to the electric field with velocities of the order of 10^-3 m/s. This is the electron drift velocity - Electrical Resistance: - The larger the potential difference, the larger the current inside the conductor Phys 102 Alanna Houston - - - Measured in Ohms (V/A) - Meaning of resistance: for a given voltage, a larger R will produce a smaller current - How to measure V and I: - Voltmeter (analog or digital) or a CRO can measure the voltage across a resistor - The voltmeter must be connected in parallel with the resistor - - Ammeter (analog or digital) is used to measure the current passing through the resistor
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