شنبه ۲۴ شهریور ۰۳ | ۱۷:۰۵ ۱۱ بازديد
•When switch S contacts A, the field generated by the applied positive voltage creates a reverse induced voltage that initially
resists current flow
•Based on the value of inductance, as the magnetic field reaches steady-state, the reverse voltage decays
•A collapsing field is generated when applied voltage is removed (switch S contacts B), creating a forward induced voltage
that attempts to keep current flowing
•Based on the value of inductance, as the magnetic field reaches zero steady-state, the forward voltage decays
Mechanical inertia and
inductor both resist
sudden change in their
state
•If number of turns per unit length
is “n”, then N= , so:n
2 2 2
2 2 20
0 0
( )n r
L n r n A
–A = cross-sectional area of coil.
–If a magnetizable material forms
the core of coil, then permeability
will be larger than .
2 2
0 N r
L
– = permeability of free space
– N = number of turns in coil
– = length of resistance-less wire
used in coil
– = radius of coil cross section.
r
0
•Antenna coil
–contains an iron core that
magnifies magnetic field
effects
–used to tune in ultra-
high-frequency signals, i.e.
RF signals
•Tuning coil
–screw-like “magnetic field
blocker” that can be adjusted to
select the desired inductance value
–used in radio receivers to select a
desired frequency.
•Chokes
–general-purpose inductors
that act to limit or suppress
fluctuating current.
–some use a resistor-like color
code to specify inductance
values.
•Toroidal coil
–resembles a donut with a
wire wrapping
–high inductance per
volume ratios, high quality
factors, self-shielding, can
be operated at extremely
high frequencies
•Isolation
–acts exclusively as an
isolation device; does not
increase or decrease the
secondary voltage
–usually come with an
electrostatic shield
between the primary and
secondary. Often come
with a three-wire plug and
receptacle that can be
plugged directly into a
power outlet
•High Frequency
–often come with air
or powered-iron cores
–used for high
frequency applications,
i.e. matching RF
transmission lines to
other devices
(transmission line to
antenna)
•Audio
–used primarily to
match impedances
between audio
devices
–work best at audio
frequencies from
150Hz to 12kHz
–come in a variety of
shapes and sizes,
typically contain a
center tap
•The algebraic sum of voltage around a
loop is zero.
•Assumption:
–Voltage drop across each passive
element is in the direction of current
flow.
1 2 3 4 0V V V V
+ V2 -
- V4 +
+ V3 1
+ V1 -
-
I
•Algebraic sum of all currents
entering and leaving a nod
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