Magnetic
fields
Magnetic
flux density (also called the B-field) is defined as
the force acting per unit current length.
Force
on a current-carrying conductor in a magnetic field :
and
Magnitude
of
(
Experiment
) Explanation
Force
on a moving charged particle in a magnetic field
Circulating
Charges
:
Calculation
of magnetic flux density
:
(1)
Magnetic fields around a long straight wire carrying current I:
where
a = perp. distance from a very long straight
wire
(2)
Magnetic fields inside a long solenoid, carrying current
I :
B = mo
n I where n
= number of turns per unit length.
Hall
effect :
At equilibrium, 
and
VH = B v d
The
current in a material is given by
I = nQAv
Substituting
for v we get 
But
A = d X t where t is the thickness
of the Hall slice.
Therefore
The
forces between two current-carrying conductors :
The
torque on a rectangular coil in a magnetic field
If the coil is in a radial
field and the plane of the coil is always
parallel
to the field, then
T
= N I A B sin θ
= N I A B sin
90o
= N I A B
Current Sensitivity
Suggested
solutions to Exercise (Magnetic Field )
