Rate in Electrical Systems 3.3

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