# Angular momentum of a solenoid

## Main Question or Discussion Point

imagine a very long solenoid with radius R ,n turn per unit length , carry current I.coaxial with the solenoid are two long cylinder shell of length L-one ,inside the solenoid at radius a ,carries a charge +Q,uniform distributed over its surface;the other ,outside the solenoid at radius b,carries charge -Q. when the current in the solenoid is gradually reduce , the cylinder begin to rotate.
WHERE DOES THE ANGULAR MOMENTUM COME FROM ???

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when current gradually reduce,the magnetic field changes,provides lorentz force(biot savrat rule),it accelerates charge particle,since cylinders are base for those particles feel force of the lorentz,thats the way angular momentum comes from ,
i have not tried to look geometrically,

Initially there are no currents. So there is no Lorentz force. There is a radial electric field between the two charged cylinders, and an axial magnetic field in the solenoid. When the magnetic field is reduced, the dB/dt induces a tangential eddy current in the inner cylinder, if it is a conductor. There will be a radial force (Lorentz I x B force) on the inner cylinder if it is a conductor, but no tangential force. The Lorentz force, because it is perpendicular to the current direction, can not "accelerate" it.

i am a high school student and lack many terminologies,i also donot know whether the charge particles at rest acted by changing magnetic field will feel force and if it feels in what direction
here, when current is flowing through cylinder, the magnetic field is parellel to tangent on the surface of cylinder, and we we can clearly that the changing magnetic flux is travelling from one end of cylinder to other end

now according to my book by right hand first rule , when magnetic field travels in thumb directin current should flow in in the direction in which other finger curls, since charge particles Q and -Q are also medias of current , they need to flow as per the right hand first rule which makes cylinder rotate and i donot what the force is called, lorentz or other because charge particle in rest or may be its lorentz force considered due to changing magnetic field which enhances relative motion between charge particle and magnetic flux(thus relative velocity) .
what ever because since i am high school student i donot know exact mechanism of geometry of lorentz force direction but i know that that tthe force comes due to the interaction of magnetic feild of charge particles and acting magnetic feild, this is how i understood
if u have any commentpls reply bob s