Lenz's Law: Understanding A-level Physics Problem

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SUMMARY

Lenz's Law asserts that an induced electromotive force (EMF) opposes the change that causes it. In the context of a magnet falling through a coil within an open circuit, an EMF is generated, but no current flows, resulting in the magnet accelerating downward at gravitational acceleration (g). This scenario illustrates a common misconception about Lenz's Law, emphasizing that the induced current, not the EMF itself, is responsible for opposing changes. The discussion clarifies that without a closed circuit, the expected opposing force does not manifest.

PREREQUISITES
  • Understanding of Lenz's Law in electromagnetism
  • Basic knowledge of electromotive force (EMF)
  • Familiarity with magnetic fields and their interactions with conductors
  • Concept of electric circuits, particularly open and closed circuits
NEXT STEPS
  • Study the principles of electromagnetic induction and Faraday's Law
  • Explore the relationship between current, voltage, and resistance in circuits
  • Investigate the effects of magnetic fields on moving charges
  • Learn about practical applications of Lenz's Law in electrical engineering
USEFUL FOR

A-level physics students, educators teaching electromagnetism, and anyone seeking to deepen their understanding of electromagnetic principles and circuit behavior.

padraig
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Hi, I'm just doing my A-level physics revision and there's something I'm a bit unsure about. Lenz's law states that an induced EMF will always act to appose the change that is causing the EMF in the first place. However, if we take the example of a magnet falling through a coil that is part of a circuit which has a gap in it, then an EMF is still said to be produced but there is no current. The magent in this case falls to ground with unchanged acceleration g. Surely though, if Lenz's law holds true and it is the EMF that opposes changes, then the magnet's acceleration downwards would be decreased just as it would if the circuit was complete.

Any ideas would be of great help, thanks

Pat
 
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padraig said:
Hi, I'm just doing my A-level physics revision and there's something I'm a bit unsure about. Lenz's law states that an induced EMF will always act to appose the change that is causing the EMF in the first place. Pat
That's a mis-statement of Lenz's law. The induced current will appear in such a direction that it opposes the change that produced it.
 

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