Transcript Inductor Inductor • An inductor is a device that temporarily resists change in current flow. • http://www.falstad.com/circuit/einduct.html (Please try this applet)

Inductor
Inductor
• An inductor is a device that
temporarily resists change in current
flow.
• http://www.falstad.com/circuit/einduct.html (Please try this applet)
Inductor at t=0
Inductor resists the currently initially.
VL jumps to 2.5 V because there is no current in the resistor initially.
Inductor at t>0
1. Inductor slowly gives up its resistance to current
2. Current begins to increase
3. Voltage across the resistor begins to increase while the voltage
across inductor begins to drop. (Can you explain why?)
4. What is limit of the current in the circuit?
VS transitions to 0V
What happens when VS switches from 2.5 V to 0V?
L resists change in current. So initially the resistor will carry
0.25 mA of current. Since VS is 0V, VL will be -2.5V.
The Inductor stops resistant the change in current.
The current will slowly decrease to 0.
Plot Inductor Current as a
function of time
The current in an inductor can not change
instantaneously.
Exponential Current Buildup
τ = 𝐿/𝑅
Current versus time
More details in Chapter 7
Exponential decrease of current
τ = 𝐿/𝑅
Current versus time
Why Does an Inductor Oppose
Change in Current?
Magnetic Field
(Magnetic field)
Current
Note: The field is stronger closer to the conductor and becomes weaker
with increasing distance from the conductor.
Right-Hand Rule
Thumb: Points in the direction of current
Fingers: point in the direction of the magnetic lines of force.
Reference: (Floyd, p. 384)
Different Ways of Building
Inductors on Silicon
Inductance Calculator
http://www-smirc.stanford.edu/spiralCalc.html
Cumulative magnetic force
Application: Electromagnet
When the coil of wire is connected to a battery, there is current.
A magnetic field is established.
Faraday’s observation
• A changing magnetic field can induce
a voltage in a conductor.
Faraday’s First Observation
The amount of voltage induced in a coil is directly proportional to the rate of
change of the magnetic field with respect to the coil.
Faraday’s second observation
The amount of voltage induced in a coil is directly proportional to the number
of turns of wire in a coil.
The induced current generates a voltage across the input resistance of the
voltmeter.
Lenz’ law
When an emf is generated by a change in magnetic flux according to
Faraday's Law, the polarity of the induced emf is such that it produces
a current whose magnetic field opposes
the change which produces it.
http://hyperphysics.phy-astr.gsu.edu/HBASE/electric/farlaw.html#c2
Mathematical Definition
Inductors Connected in Series
Inductors Connected in Parallel
Derivations
• Details shown in class
Use an Impedance Analyzer to
Measure Inductance