Rate in Electrical Systems

1
Rate in Electrical Systems
3.3
2
Electric Current

• Rate of electrical charge flow
• Voltage is the prime mover
• I ?q/ ?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

3
Measuring Current and Voltage

• Measure current with an ammeterseries connection
• Measure potential difference with a
  voltmeterparallel connection

4
The Speed of Charge Flow

• Electric fields travel at almost the speed of
  lightelectrons travel much slower

5
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

6
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.

7
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
  conductorwe just factor in the drift velocity.

8
AC Circuits, Frequency, and Period

• 60 cycle Alternating Current in U.S. and Canada
• Frequencyhow often a pattern repeats
  itselfmeasured in hertz (Hz)
• F n/?t (frequency equals the number of cycles
  divided by the time interval.)

9
AC Circuits, Frequency, and Period

• 1 Hz 1 cycle/sdrop cycle
• 1 Hz 1 s-1
• 1 Hz 1/1s
• Period
• The time it takes for one complete cycleseconds
  (s)
• Period and frequency are reciprocals
• T 1/f f 1/T