Transcript Rate in Electrical Systems

Rate in Electrical Systems
3.3
Electric Current
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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
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Measure current with an ammeter—
series connection
Measure potential difference with a
voltmeter—parallel connection
The Speed of Charge Flow
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Electric fields travel at almost the speed
of light—electrons travel much slower
How Charge Moves
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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
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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
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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
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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
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1 Hz – 1 cycle/s—drop cycle
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Period
• 1 Hz = 1 s-1
• 1 Hz = 1/1s
• The time it takes for one complete cycle—
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seconds (s)
Period and frequency are reciprocals
T = 1/f
f = 1/T