How Does a Rail Gun Work Without an External Magnetic Field?

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SUMMARY

The discussion centers on the operation of a rail gun without an external magnetic field, specifically addressing the role of induced electromotive force (emf) and current in the conductive rod between the rails. It is established that even in the absence of an external magnetic field, the change in magnetic flux is not instantaneous, allowing for a transient effect that induces a force on the rod. The induced current generates its own magnetic field, contributing to the overall dynamics of the system. This phenomenon highlights the complexities of electromagnetic interactions in rail gun mechanics.

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  • Understanding of Faraday's Law of Electromagnetic Induction
  • Familiarity with Lenz's Law and its implications
  • Basic knowledge of electromagnetic fields and forces
  • Concept of transient effects in electrical circuits
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Physics students, electrical engineers, and enthusiasts interested in electromagnetism and the mechanics of rail guns will benefit from this discussion.

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http://www.brightstorm.com/science/physics/magnetism/faradays-law-lenzs-law/#

Start at about 7:10 and watch until about 8:20.
I can see that an emf and hence a current will be induced in the rod between the two rails BUT if there is no external magnetic field (the magnetic field generated by the rod due to the current flowing in it is irrelvant) then why would the rod experience a force...

the only explanation I can think is that the change in magnetic flux is NOT instantaneous...therefore as it is reducing (might take 0.1 ms to completely dissapear) there is still some flux to apply a force to the rod...is this correct?
 
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Um - the example in the video has an external field.
When you switch the field off, the flux through the loop goes to zero - creating an EMF, which gives the rod (and everything else) a kick.

The transient effect for these things is usually quite complicated and a bit beyond the level of the video. For instance, as you have noted, the induced current also has a magnetic field.
 

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