inductor. an inductor is a device that temporarily resists change in current flow. induct.html...

Inductor

Inductor

• An inductor is a device that temporarily resists change in current flow.

• http://www.falstad.com/circuit/e-induct.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 current2. Current begins to increase3. Voltage across the resistor begins to increase while the voltageacross 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 carry0.25 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 changeinstantaneously.

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

Note: The field is stronger closer to the conductor and becomes weakerwith increasing distance from the conductor.

Current

(Magnetic field)

Right-Hand Rule

Thumb: Points in the direction of currentFingers: 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 numberof turns of wire in a coil.The induced current generates a voltage across the input resistance of the voltmeter.

Lenz’ law

http://hyperphysics.phy-astr.gsu.edu/HBASE/electric/farlaw.html#c2

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.

Mathematical Definition

Inductors Connected in Series

Inductors Connected in Parallel

Derivations

• Details shown in class

Use an Impedance Analyzer to Measure Inductance