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1.9.4 A Current-carrying Conductor Placed in a Magnetic Field
When a conductor carrying current is placed in a magnetic field it
experiences a force. The force acts in a direction perpendicular to both the
magnetic field and the current.
In Fig. 1.6 a conductor is shown placed perpendicular to the direction of
magnetic field. Such a conductor in cross-sectional view has been shown by a
small circle. The dot inside the small circle indicates that current is flowing
towards the observer. The conductor will experience a force in the upward
direction as has been shown. If the direction of current through the conductor
is reversed, the force on the conductor will be in the downward direction.
The force on the conductor will depend upon the flux, ϕ or flux density,
where A is the area of the magnetic poles. The force will also
depend upon the effective length of the conductor in the magnetic field, i.e., ℓ
on the magnitude of current flowing, i.e., I. The force developed is expressed
as
F = BI ℓ Newtons (1.22)
Here the current-carrying conductor and the magnetic fields are at right
angles to each other. If, however, the conductor is inclined with the magnetic
field by an angle θ, then the length of the conductor perpendicular to the
magnetic field is to be considered as shown in Fig. 1.7. The length of the
conductor perpendicular to the magnetic field is ℓ Sinθ. Thus, the general
expression for force F is
F = BI ℓ Sinθ Newton (1.23)
The direction of the force is determined by applying Fleming’s left-hand-rule
which is stated as:
