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Rate in Electrical Systems. 3.3. Electric Current. Rate of electrical charge flow Voltage is the prime mover I = Δ q/ Δ t (electric current equals charge moved divided by the time interval) Charge is measured in Coulombs (C); current is measured in amperes (A). 1A = 1C/s.
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Electric Current • Rate of electrical charge flow • Voltage is the prime mover • I = Δq/ Δt (electric current equals charge moved divided by the time interval) • Charge is measured in Coulombs (C); current is measured in amperes (A). 1A = 1C/s
Measuring Current and Voltage • Measure current with an ammeter—series connection • Measure potential difference with a voltmeter—parallel connection
The Speed of Charge Flow • Electric fields travel at almost the speed of light—electrons travel much slower
How Charge Moves • The metal conductor has free electrons that have gained enough energy to break their bonds with the metal atoms in the conductor. • The conductor is neutral, so every free electron leaves behind a positive ion
How Charge Moves • The free electrons move through the conductor, bouncing around from collisions between the other free electrons and the positive ions. • When an electric field (voltage) is applied to the conductor, a force is exerted on the free electrons. The force accelerates the electrons between collisions, resulting in a net displacement (drift) of the electrons in the direction of the force.
How Charge Moves • Drift velocity in the conductor is very slow because collisions interrupt the paths of free electrons. • We usually think of current in terms of electrons moving in a straight path through the conductor—we just factor in the drift velocity.
AC Circuits, Frequency, and Period • 60 cycle Alternating Current in U.S. and Canada • Frequency—how often a pattern repeats itself—measured in hertz (Hz) • F = n/Δt (frequency equals the number of cycles divided by the time interval.)
AC Circuits, Frequency, and Period • 1 Hz – 1 cycle/s—drop cycle • 1 Hz = 1 s-1 • 1 Hz = 1/1s • Period • The time it takes for one complete cycle—seconds (s) • Period and frequency are reciprocals • T = 1/f f = 1/T