January 12th in 1832 Michael Faraday did the following experiment in London:

He placed two copperplates in the Thames river at opposite ends of a bridge crossing at 300m apart. He then connected these copperplates with insulated wires to a voltage meter.
He measured a 19mV voltage. Magnetic field in London is measured to be 43µT (43*10^-6 T) and inclination is 71 degrees.

Why did Faraday's meter measure a voltage and what was the velocity of the water in the river Thames at that time?

Hello

my English is not so good. I can not understand what inclination is 71 degrees mean  so i am not going to involve it.

Solution:

While the water is moving the free electrons are also moving { with the same speed (u) } .
So it is applied to each electron a Lorentz force (Fl) cause of the magnetic field. So the electrons are  moving to the one copperplate which is being charged with -Q while the other copperplate is charged with +Q so detween the two plates appears an electric field which we can say that it is homogenous so an electric force is now also applied to the electrons (Fel) .
The charge stops when : Fl.=Fel.

{ (B^u)=90 degrees }
(Fl.=B*u*q , q=e )
(Fel.=E*q , q=e )

B*u*e=E*e
B*u=E  the electric field is homogenous so :   E=V:L

B*u=V:L

u=V:L*B    (V=19*10^-3 V)
                (L=300 m)
                (B=43*10^-6 T)

u=190:149 m:s so water's speed is 190:149 m:s

Thoughts:
In this experiment electricity appeared ??
The circuit is connected to the earth through the water.

Posted by Brett on 2007-05-28 15:23:58