E X P E R I M E N T L
Keele University Physics/Astrophysics Laboratory
School of Physical and Geographical Sciences Experimental Scripts
79
Hall Effect
1. Introduction
A magnetic field applied to a current carrying material exerts a force on the charge carriers.
This leads to build up of an electric field EH (Figure 1) across the material (hence the build up of the
potential difference between top and bottom face of the conductor), known as the Hall effect.
2. Theory
Figure 1: Hall Effect (From University Physics, Benson)
I – Current in x-direction;
B – Magnetic field in y-direction (i.e. perpendicular to the slab);
vd – Drift velocity;
W – Width of the conductor;
t – Thickness of the conductor.
The force FB is in the
z
-direction for a positive charge and is given by:
FB = q v x B (1)
Due to this force, there will be a net drift of the positive charges towards the top face of the
conductor as shown in Figure 1. Assume that the electric field due to this drift is EH (EH = VH/W)
and produces a force FE on the charge carriers in the opposite direction to FB and given by:
FE = qEH (2)
As the potential difference (VH) builds up, FE increases until FE (qEH)= FB (qvdB). Therefore,
since the net force on the charge carrier is zero, this leads to the end of charge migration (i.e. steady
state).
At the steady state:
FE = FB
