From electric to electronic
Electric circuits are connections of
conductive wires and other devices whereby the uniform flow of electrons
occurs. Electronic circuits add a new dimension to electric circuits in
that some means of control is exerted over the flow of electrons
by another electrical signal, either a voltage or a current.
In and of itself, the control of electron
flow is nothing new to the student of electric circuits. Switches
control the flow of electrons, as do potentiometers, especially when
connected as variable resistors (rheostats). Neither the switch nor the
potentiometer should be new to your experience by this point in your
study. The threshold marking the transition from electric to electronic,
then, is defined by how the flow of electrons is controlled
rather than whether or not any form of control exists in a circuit.
Switches and rheostats control the flow of electrons according to the
positioning of a mechanical device, which is actuated by some physical
force external to the circuit. In electronics, however, we are dealing
with special devices able to control the flow of electrons according to
another flow of electrons, or by the application of a static voltage. In
other words, in an electronic circuit, electricity is able to control
electricity.
Historically, the era of electronics
began with the invention of the Audion tube, a device controlling
the flow of an electron stream through a vacuum by the application of a
small voltage between two metal structures within the tube. A more
detailed summary of so-called electron tube or vacuum tube
technology is available in the last chapter of this volume for those who
are interested.
Electronics technology experienced a
revolution in 1948 with the invention of the transistor. This
tiny device achieved approximately the same effect as the Audion tube,
but in a vastly smaller amount of space and with less material.
Transistors control the flow of electrons through solid semiconductor
substances rather than through a vacuum, and so transistor technology is
often referred to as solid-state electronics.
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