- Direct Current Resistance
Current Resistance ¡V The DCR is defined as the
resistance of an inductor as a result of the resistance
of the wire used in the winding.
Objects such as wires that are designed to have low resistance
so that they transfer current with the least loss of electrical
energy are called conductors. Objects that
are designed to have a specific resistance so that they
can dissipate electrical energy or otherwise modify how
a circuit behaves are called resistors.
Conductors are made of highly conductive materials such
as metals, in particular copper and aluminium. Resistors,
on the other hand, are made of a wide variety of materials
depending on factors such as the desired resistance, amount
of energy that it needs to dissipate, precision, and cost.
The resistance of a given resistor or conductor grows with
the length of conductor and specific resistivity of the
material, and decreases for larger cross-sectional area.
The resistance R and conductance G of a conductor of uniform
cross section. Resistivity is a measure of the material's
ability to oppose electric current.
A wire carrying alternating current has a reduced effective
cross sectional area because of the skin effect. Adjacent
conductors carrying alternating current have a higher resistance
than they would in isolation or when carrying direct current,
due to the proximity effect. At commercial power frequency,
these effects are significant for large conductors carrying
large currents, such as busbars in an electrical substation
or large power cables carrying more than a few hundred amperes.
When an alternating current flows through the circuit, its
flow is not opposed only by the circuit resistance, but
also by the opposition of electric and magnetic fields to
the current change. That effect is measured by electrical
reactance. The combined effects of reactance and resistance
are expressed by electrical impedance.