Magnetic Forces, Materials and Inductance Force On A Moving Charge Force on a Differential Current Force And Torque On A Closed Circuit Force And Torque On A Closed Circuit The Nature of Magnetic Materials

1. “THE NATURE OF MAGNETIC
MATERIAL FORCE & TORQUE ON
CLOSED CIRCUIT”
 PREPARED BY :
DISHANT PATEL S. 140123109009
VISHAL GOHEL R. 140123109003
JAY PANCHAL H. 140123109007
 GUIDED BY : Prof. Yogesh patel

2. Magnetic Forces, Materials and Inductance
The magnetic field B is defined from the Lorentz Force Law,
and specifically from the magnetic force on a moving charge:
F = qv x B
1. The force is perpendicular to both the velocity v of the charge
q and the magnetic field B.
2. The magnitude of the force is F = qvB sin where is the angle
< 180 degrees between the velocity and the magnetic field. This
implies that the magnetic force on a stationary charge or a
charge moving parallel to the magnetic field is zero.
3. The direction of the force is given by the right hand rule. The
force relationship above is in the form of a vector product.

3. From the force relationship above it can be deduced that the
units of magnetic field are Newton seconds /(Coulomb meter)
or Newton per Ampere meter. This unit is named the Tesla.
It is a large unit, and the smaller unit Gauss is used for small
fields like the Earth's magnetic field. A Tesla is 10,000 Gauss.
The Earth's magnetic field is on the order of half a Gauss.

4. Force On A Moving Charge
 Lorentz Force Law
• Both the electric field and magnetic field can be defined from
the Lorentz force law:
• The electric force is straightforward, being in the direction of
the electric field if the charge q is positive, but the direction of the
magnetic part of the force is given by the right hand rule.

5. Force On A Moving Charge

6. Force on a Differential Current
dF = dQv x BJ ρv v⋅
dF J Bdv× dQ ρv dv⋅
dF ρv dv⋅ v⋅ B×
dF J Bdv×
Jdv KdS IdL
dF K BdS×
dF IdL B×
F vJ B×
⌠

⌡
d
vol
F SK B×
⌠

⌡
d
S
F LI
⌠

⌡
d B× I− LB_x_
⌠

⌡
d⋅
F IL B×

7. Force And Torque On A Closed Circuit
F I− LB_x_
⌠

⌡
d⋅
F IB− L1
⌠

⌡
d×
T R F×

8. Force And Torque On A Closed Circuit
dT IdS B×
Magnetic Dipole Moment dm
dm IdS
dT dm B×
T IS B× m B×

9. Force And Torque On A Closed Circuit
DC Motor - Illustration

10. The Nature of Magnetic Materials
Magnetic Materials
 Magnetic Materials may be classified as diamagnetic,
paramagnetic, or ferromagnetic on the basis of their
susceptibilities.
 Diamagnetic materials, such as bismuth, when placed in an
external magnetic field, partly expel the external field from within
themselves and, if shaped like a rod, line up at right angles to a
non-uniform magnetic field. Diamagnetic materials are
characterized by constant, small negative susceptibilities, only
slightly affected by changes in temperature.

11.  Paramagnetic materials, such as platinum, increase a
magnetic field in which they are placed because their atoms have
small magnetic dipole moments that partly line up with the
external field.
 Paramagnetic materials have constant, small positive
susceptibilities, less than 1/1,000 at room temperature, which
means that the enhancement of the magnetic field caused by the
alignment of magnetic dipoles is relatively small compared with
the applied field.
Paramagnetic susceptibility is inversely proportional to the
value of the absolute temperature. Temperature increases cause
greater thermal vibration of atoms, which interferes with
alignment of magnetic dipoles.

12.  Ferromagnetic materials, such as iron and cobalt, do not have
constant susceptibilities; the magnetization is not usually
proportional to the applied field strength.
 Measured ferromagnetic susceptibilities have relatively large
positive values, sometimes in excess of 1,000. Thus, within
ferromagnetic materials, the magnetization may be more than
1,000 times larger than the external magnetizing field, because
such materials are composed of highly magnetized clusters of
atomic magnets (ferromagnetic domains) that are more easily
lined up by the external field.