Last Updated: Tue Apr 9 01:50:46 PM CDT 2024
Full Circle
- A current will produce a magnetic field.
- A magnetic field can create current…
Demos
Demo
We can generate electricity with a coil of wire and a magnet.
We don’t actually need a magnet, we just need a magnetic field.
We get an induced current when the magnetic field changes.
We can amplify the current with iron
We are just generating electricity
and in fact, this is the principle used by all power plants.
Applications
Applications
Electrical Generator
- Spin a coil of wire in a magnetic field, or spin a magnet near a coil of wire, and we can generate AC electricity.
Wireless Power
- With induction, we can induce current in a loop without connecting it to an emf. We induce the emf in the loop.
Audio
- If we wiggle a magnet inside a coil of wire, it will induce a voltage.
- If the magnet is attached to a diagram, we can wiggle it with sound waves.
Electromagnetic Pulse (EMP)
If the magnetic field in a region of space containing a loop of wire changes, an emf will be induced in the loop of wire.
- Captain America: Civil War, Independence Day: Resurgence, Godzilla, Pacific Rim, Red Dawn, The Dark Knight Rises, Cars 2, Superman Returns, The Matrix, GoldenEye
Applications: Generating Electricity
Applications: Generating Electricity
Hydroelectric Power: Use running water to turn a turbine to turn a generator
Applications: Generating Electricity
Natural Gas Power: Burn natural gas to run an engine to turn a generator.
Applications: Generating Electricity
Wind Power: Use a windmill to turn a generator.
Applications: Generating Electricity
Coal Power: Burn Coal to produce steam to turn a turbine to turn a generator
Applications: Generating Electricity
Nuclear Power: Fission Uranium to produce heat to produce steam to turn a turbine to turbine to turn a generator
Applications: Wireless Power
With induction, we can induce current in a loop without connecting it to an emf. We induce the emf in the loop.
Applications: Wireless Power
Applications: Audio - Microphone
A microphone produces an electric signal from an audio signal by inducing a current that can be measured.
In fact, if we run current through the coil, we have a speaker.
Applications: Audio - Magnetic Tape
We even use induction for (old) magnetic tapes 
Theory
Faraday’s Law of Induction
Magnetic Flux
Flux is a measure of the field passing through a surface.
Conceptually, it is directly related to the number of field lines that pass through a surface.
Note the dot product, it is:
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Lenz’s Law
The direction of the induced emf drives current around a wire loop to always oppose the change in magnetic flux that causes the emf.
Lenz’s Law
The direction of the induced emf drives current around a wire loop to always oppose the change in magnetic flux that causes the emf.
- Magnetic field lines through a wire loop give a magnetic flux.
- If this magnetic flux changes, it will induce a current.
- The induced current will create an induced magnetic field.
- If the magnetic flux is increasing, the induced field points in the opposite direction of the external field.
- If the magnetic flux is decreasing, the induced field points in the same direction as the external field.
- The second right-hand rule, with the thumb pointed in the direction of the induced field, gives the direction of the current.
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A current runs through coil A counterclockwise (when viewed from the amazingly detailed drawing of an eye). If this increases from 0 A to 1 A, what direction will the induced current in coil B flow?
A. Clockwise
B. Counter-Clockwise
C. Up
D. Down |
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A current runs through coil A counterclockwise. If this decreases from 1 A to 0 A, what direction will the induced current in coil B flow?
A. Clockwise
B. Counter-Clockwise
C. Up
D. Down |
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A current runs through coil B clockwise. If this increases from 1 A to 2 A, what direction will the induced current in coil A flow?
A. Clockwise
B. Counter-Clockwise
C. Up
D. Down |
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Ring Launcher
- We now know enough physics to explain the ring launcher
- Current runs through a solenoid
- This current generates a magnetic field
- The magnetic field is strengthened by the iron core
- A current is induced in the ring
- The magnetic field of the solenoid exerts a force on this current.
- This current creates a magnetic field
- The magnetic field points in the opposite direction of the external magnetic field
- This is just like putting two bar magnets together
- It does not matter what direction current runs through the solenoid
Examples
Faraday’s Law of Induction
Magnetic Flux
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Examples
As usual, some of these examples are contrived.
But that is so we can actually do some calculations.
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Electric Generator
A circular coil of wire containing \(N\) loops with diameter \(D\) rotates at a constant rate in a region of uniform magnetic field with magnitude \(B\). The loop completes one revolution every \(T\) seconds. If the magnetic flux through the coil is zero at time \(t = 0\), determine the induced emf as a function of time.
- What is the peak emf that will be produced?
- What torque is required to rotate the coil at a constant speed?
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Last Slide
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There is nothing to see here!
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Look, I know that the slide count says there are more slides, but there aren’t any more.
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Seriously, its just a bunch of Last Slide slides.
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This is the last one that says anything funny. You can stop clicking now.
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Demo
We can generate electricity with a coil of wire and a magnet.
Demo
We don’t actually need a magnet, we just need a magnetic field.
Demo
We get an induced current when the magnetic field changes.
