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FUNDAMENTALS OF ELECTRIC SYSTEMS
THE MAGNETIC FIELD:
A magnetic field is defined as the space
around a magnet or a current carrying conductor. The magnetic field B is represented by lines of induction. Figure illustrates the lines of induction of a
magnetic field B near a long current carrying conductor.
The vector of the
magnetic field is related to its lines of induction in this way:
1.
The direction of B
at any point is given by the tangent to the line of induction.
2.
The number of lines of induction per unit
cross-sectional area (perpendicular to the lines) is proportional to the
magnitude of B .Magnetic field B is large if the lines are close together, and it
is small if they are far apart.
The flux of magnetic field B is given
by
The integral is taken over
the surface for which flux is defined.
The magnetic field exerts a
force on any charge moving through it. If q0 is a positive charge
moving at a velocity v in a magnetic field B, the force F acting on the charge Figure is given by:
The magnitude of the force F
is given by:
Where (sine) is the angle
between v and B.
The force F will always be at a right angle to the plane
formed by v and B. Thus, it will always be a
sideways force. The force will disappear in these cases:
1. If the charge stops moving
2. If v is parallel or anti parallel
to the direction of B
The force F has a maximum
value if v is at a right angle to B (angle =
90).
Figure illustrates the force
created on a positive and a negative electron moving in a magnetic field B pointing out of the plane of the figure. The
unit of B is the tesla (T) or weber per square meter (Wb/m2).
Thus,
The force acting on a
current-carrying conductor placed at a right angle to a magnetic field B is
given by:
F = ilB
Where l is the length
of conductor placed in the magnetic field.
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