physicist J.J. Thompson.
Because of the electric field built up across the conducting strip, there is a potential difference across
the strip. It is straightforward to calculate the magnitude of this potential difference: charges will build up
across the strip until the the magnetic forceqvdBis balanced by the electrostatic forceqE, wherevdis
the drift velocity,qis the charge on the particles carrying the current, andBandEare the magnetic and
electric field strengths, respectively. Since in equilibrium the forces will balance,qvdBDqE,orEDvdB.
The potential difference"Hacross the strip is then"Hw, wherewis the width of the strip. Therefore this
potential, called theHall emfis given by
"HDvdBw (32.7)Besides its historical interest, the Hall effect can be used today as a means of measuring magnetic field
strength. We measure the strip widthw, and we can determine the drift velocityvdby calibration in a known
magnetic field. Then Eq. (32.7) can be used to determine the magnetic field strengthBby measuring the
Hall emf"H.