Active Versus Passive Components
A passive component either consumes (but does not
produce) energy, is incapable of power gain, or both.
An active component is capable of gain (amplification)
and possibly directionality. More sophisticated active
components can even add intelligence in some manner to
the signal or data passing through or being controlled by it.
These are the most common passive components.
Carbon composition resistors have solid cylindrical
resistive elements with embedded metal end caps and
attached lead-out wires, (Figure 2). Paint or plastic
protects them. The resistive element is finely powdered
carbon with an insulating material (usually ceramic).
A resin bonds this mixture together.
The ratio of the fill material (the powdered ceramic)
and the carbon determines its resistance. Higher carbon
concentrations have lower resistances. These resistors
were predominate until the 1960s. Manufacturing
advances allowed other technologies with better
specifications such as tolerance, voltage dependence,
and stress to substantially gain greater market share.
Depositing this on an insulating substrate and cutting
a spiral in it creates a long, narrow resistive path as shown
in Figure 3. Varying shapes coupled with the resistivity of
carbon provide a variety of resistances. Resistances are
available in a range from one ohm to 10 megohms.
Resistivity is the electrical resistance of a conductor of
a defined cross-sectional area and known length made of
a certain defined material, such as carbon film. The formula
is as follows:
ρ = resistivity L = length and
A = cross-sectional area
Thick and Thin Film
Thick film resistors became popular during the 1970s,
and most SMD resistors today are of this type. The main
difference between thin film and thick film resistors is
not the actual thickness of the film, but rather how
manufacturers apply the film to the cylinder (axial lead
resistors) or the surface (SMD resistors).
Graphics provided by www.electronics-tutorials.ws, EPCOS, and
Nonmetallic Inorganic Materials Science City, ETH Zürich, MATL
Figure 2. A carbon composition resistor showings its
Figure 3. A narrow strip cut in a circular manner
around the resistor that determines a carbon film resistor's
Figure 4. A wire wound resistor partially showing its
The resistance of both thin and thick film resistors
after manufacture is not highly accurate; they are usually
trimmed to an accurate value by abrasive or laser
trimming. Thin film resistors are usually specified with
tolerances of 0.1, 0.2, 0.5, or 1%, and with temperature
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