How does coil gun works ?

By:Prayag nao

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How does coil gun works ?.
Have you ever think about it,Probably yes,if not don't worry i will tell you working of coil gun.Before we start to learn coil gun working,we have to know some basics phenomena behined it.Let's start........

Magnetic Field of Current

The magnetic field lines around a long wire which carries an electric current form concentric circles around the wire. The direction of the magnetic field is perpendicular to the wire and is in the direction the fingers of your right hand would curl if you wrapped them around the wire with your thumb in the direction of the current.

 


The magnetic field of an infinitely long straight wire can be obtained by applying Ampere's law. The expression for the magnetic field is
 

Magnetic Field of Current Loop

Examining the direction of the magnetic field produced by a current-carrying segment of wire shows that all parts of the loop contribute magnetic field in the same direction inside the loop.
Electric current in a circular loop creates a magnetic field which is more concentrated in the center of the loop than outside the loop. Stacking multiple loops concentrates the field even more into what is called a solenoid.



Field at Center of Current Loop

The form of the magnetic field from a current element in the Biot-Savart law becomes
which in this case simplifies greatly because the angle =90 ° for all points along the path and the distance to the field point is constant. The integral becomes


It's enough for understanding working of coil gun,Now it's time to come on our main topic.........

  A coilgun is a series of coils that are successively energized as a conductive projectile made from magnetic material passes by them.

coilgun 

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Each stage acts on similar principles to those of a solenoid. Current loops induce magnetic flux through their center:

http://en.wikipedia.org/wiki/File:VFPt_Solenoid_correct2.svg 

As the conductive projectile approaches the air-core current loops, two things happen: the loop inductance increases and the projectile becomes magnetized. The magnetized projectile is then attracted to the loop magnetic field, accelerating towards it. As it approaches, inductance increases, completing a positive feedback loop such that the pull on the projectile and magnetic field created by the loops increase.

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This process reaches a peak when the projectile is completely enclosed by the coil, where further travel decreases the loop's inductance. At this point, current through the loop is abruptly turned off so the projectile won't be slowed down by its continued attraction to the coil's magnetic field.
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If you have any query please comment below....................

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