A Hall probe is placed in a magnetic field. The Hall voltage is zero. The Hall probe is rotated to a new position in the magnetic field. The Hall voltage is now maximum. Explain these observations.
The formula for calculating the Hall voltage 
as measured by a Hall probe is
The table below shows the value of 
for two materials.
State the meaning of .
Explain why a Hall probe is made from silicon rather than copper.
A Hall probe gives a maximum reading of 
when placed in a uniform magnetic field of flux density 
. The same Hall probe is then placed in a magnetic field of fixed direction and varying flux density. The Hall probe is in a fixed position so that the angle between the Hall probe and the magnetic field is the same as when the Hall voltage was . The variation of the reading on the Hall probe with time 
from time 
to time 
is shown in the graph below.
A coil with 780 turns and a diameter of 
is placed in this varying magnetic field. The plane of the coil is perpendicular to the field lines. Calculate the magnitude of the maximum electromotive force (e.m.f.) induced in the coil in the time between and .
.
