Properties of an
The properties of inductors derive from a different type of
force than the one we invented charge to explain: magnetic
force rather than electric force.
When current flows through a coil (or any wire) it produces
a magnetic field in the space outside the wire, and the coil
acts just like any natural, permanent magnet, attracting
iron and other magnets.
How Inductor Works?
If you move a wire through a magnetic field, a
current will be generated in the wire and will flow through the
associated circuit. It takes energy to move the wire through the
field, and that mechanical energy is transformed to electrical
energy. This is how an electrical generator works.
If the current
through a coil is stopped, the magnetic field must also disappear,
but it cannot do so immediately. The field represents stored energy
and that energy must go somewhere. The field contracts toward the
coil, and the effect of the field moving through the wire of the
coil is the same as moving a wire through a stationary field: a
current is generated in the coil.
This induced current acts to keep
the current flowing in the coil; the induced current opposes any
change, an increase or a decrease, in the current through the
inductor. Inductors are used in circuits to smooth the flow of
current and prevent any rapid changes.
The current in an inductor is analogous to the voltage across a
capacitor. It takes time to change the voltage across a capacitor,
and if you try, a large current flows initially.
Similarly, it takes
time to change the current through an inductor, and if you insist,
say by opening a switch, a large voltage will be produced across the
inductor as it tries to force current to flow.
Such induced voltages
can be very large and can damage other circuit components, so it is
common to connect some element, like a resistor or even a capacitor
across the inductor to provide a current path and absorb the induced
voltage. (Often, a diode, which we will discuss later, is used.)
There are almost no inductors on the
RoboBoard, but you will be using some indirectly: the motors act
like inductors in many ways. In a sense an electric motor is the
opposite of an electrical generator.
If current flows through a wire that
is in a magnetic field (produced either by a permanent magnet or
current flowing through a coil), a mechanical force will be
generated on the wire. That force can do work.
In a motor, the wire that moves
through the field and experiences the force is also in the form of a
coil of wire, connected mechanically to the shaft of the motor. This
coil looks like and acts like an inductor; if you turn off the
current (to stop the motor), the coil will still be moving
through the magnetic field, and the motor now looks like a generator
and can produce a large voltage. The resulting inductive voltage
spike can damage components, such as the circuit that controls the
Measurement of Inductance
Inductors are measured in henrys (h), another very big unit, so you
are more likely to see millihenries, and microhenries.