Slide 1
Changing magnetic flux through a loop can induce voltage
Magnetic flux measures the magnetic field passing through an area. Changing the flux through a conducting loop can induce voltage around it. This is electromagnetic induction.
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Flux depends on field strength, loop area and orientation. Moving a magnet is one way to change it, but rotating the loop or changing the field electrically can also produce induction.
Slide 2
Faster flux change produces more induced voltage
Faster change in magnetic flux produces a larger induced voltage under otherwise comparable conditions. A stationary unchanging flux produces no such loop voltage.
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A coil with multiple turns adds the induced effects when the turns are linked similarly. This helps explain why coils rather than single wires are common in practical induction devices.
Slide 3
The induced current opposes the change that caused it
When an induced current flows, its magnetic effect opposes the flux change that produced it. This direction rule is called Lenz’s law.
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Opposition is to the change, not necessarily to the original field. If an applied field is decreasing, the induced current can act to sustain it rather than reverse it.
Slide 4
A generator draws mechanical work from its driver
A generator can turn mechanical motion into electrical energy through induction. Drawing current creates a reaction that resists the driving motion.
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Turning a generator under load therefore requires more torque than turning it with little electrical load, aside from other losses. The electricity does not appear without an energy input to the whole system.
Slide 5
Changing coil current can induce voltage without motion
Changing current in one coil changes its magnetic field. A nearby linked coil can then receive an induced voltage even if both stay still.
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This is the basis of a transformer. A steady direct current after switching produces no continuing flux change in the ideal transformer, which is why its normal operation relies on changing current.
Sources
- Michael Faraday
US Energy Information Administration
- Basics of Electricity, Energy
National Renewable Energy Laboratory