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Registered Member #229
Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506
I am not an EE guy and probably I say some BS... If the two spheres have the same center "O", the outer sphere B will behave like all the charge will be concentrated in "O". The electric action of sphere A is ecranated by the sphere B (A only will induce through influience a charge Qa on B). So the sphere B will act as a sphere charged with Qa (through influience) + Qb (own charge), and it will be the sphere with the higher potential. Connecting the two spheres, the A sphere will be like a charged conductor inside a Faraday cage, so the charges from A will go to the external surface of B always.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
Vasil, you mention that sphere B is at the higher potential, so how can charge from A go to B? You need to clean up your answer and know why A or B is at the higher potential.
Registered Member #229
Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506
It is the same mechanism which work in a VDG sphere where the charge pass from the belt on the big collector electrode. I dont know how to explain better and maibe everything is wrong. Give the correct explanation.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
You are close, but maybe the language difference is making it harder. The potential on B (due to B alone) is kQb/R, where k is a constant. Because the electric field is zero within the hollow sphere, the potential is constant within the sphere and is imparted on the smaller sphere. Thus, the total potential on the small sphere, A, is kQa/r + kQb/R
The total potential on the larger sphere is the sum of that due to the charge on B and on A. Because the "point charge" of A is R units away from the B the total potential on B is kQa/R + kQb/R
We can see that because r < R, the absolute potential on the smaller sphere, A, will always be greater than the charge on B. If q is positive, Va - Vb will cause positive charge to flow to B no matter what charge we start out with on B. If q is negative, Va-Vb will cause negative charge to accumulate on B.
Vasil, you are right about this being the basis for the Van Der Graff. This is why the outer sphere accumulates the charge brought to the inside by the belt.
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Electrical Quizzes - QUIZ 8 POSTED
