A copper disk of `r_(0)=20cm` radius revolves in a vertical plane at 3000 r.p.m. One contact from a sensitive galvanometer is connected to the disk's axis, the other by means of a mercury contact to the outer edge of the disk (Fig.) Find the voltage.
Will the galvanometer pointer point in another direction, if the direction of rotation of the disk is changed?
The Earth's magnetic field is compensated.

Answer

`1.1xx10^(-8)V;` will not change

Explanation

Classical Electron Theory 31.2. Here the centrifugal force of inertia, `I_(cf)==momega^(2)r`, where r is the distance from the appropriate point of the conductor to the centre of the disk is the non-electrical force acting on the disk. The strength of this force field is
`E^(**)=(I_(cf))/(e)=(momega^(2)r)/(e)`
The induced c.m.f. may be found either graphically (Fig.), or by integration:

`=(momega^(2))/(e)int_(0)^(r_(0))rdr=(momega^(2)r_(0)^(2))/(2e)`