31-08-2009 magnetic field at center

This is a simple standard question... (Which I would rate as a must know for most beginners)

A disc of uniform surface charge density Ïƒ and radius r is rotated about its center, find the magnetic field induced at the center of the disc.

5 Answers

db = Î¼idl/4Ï€r²

let the angular velocity we Ï‰

Now consider a small area at distance x from the centre = 2Ï€xdx

Q=Ïƒ2Ï€xdx
i = Ï‰Ïƒxdx
db = Î¼*Ï‰Ïƒxdx*2Ï€x/4Ï€x²
b = Î¼Ï‰rÏƒ/2

The answer may be wrong since magnetism is just started by me

Awesome work virang...

Just elaborate how you found out current.. so that it becomes a bit more lucid for the other users..

Current = Q * no.of times it passes a area
i = Q*Revs
i = Q*Ï‰/2Ï€
Q = Ïƒ * 2Ï€xdx
Therefore i = ÏƒÏ‰xdx

Awesome :)

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