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Torque developed by a DC motor depends upon
magnetic field
length of the conductors
number of conductors
all of above
length of the conductors
The electromagnetic torque developed in a DC motor is directly proportional to the magnetic flux per pole, the number of armature conductors, and the armature current. Since these factors collectively define the motor's internal torque equation, the torque depends on all of the listed parameters.
The electromagnetic torque developed in a DC motor is directly proportional to the magnetic flux per pole, the number of armature conductors, and the armature current. Since these factors collectively define the motor's internal torque equation, the torque depends on all of the listed parameters.
TaтАЛ=2╧АAP╬жZIaтАЛтАЛ тАФ Fundamental electromagnetic torque equation for a DC motor
F=BIL тАФ Force on a single conductor in a magnetic field
According to the Lorentz force law, a current-carrying conductor placed in a magnetic field experiences a force F=BIl. When these conductors are placed on a rotating armature, the summation of these forces at a distance from the axis of rotation produces the developed electromagnetic torque. The total torque is defined by the motor torque equation TaтАЛ=2╧АAP╬жZIaтАЛтАЛ.
Magnetic field flux (╬ж) is provided by the field poles.
The number of armature conductors (Z) is a constructional parameter.
The physical length of the conductors (L) within the magnetic field determines the force magnitude.
Torque is also directly proportional to armature current (IaтАЛ).
Predictable relationship between flux and torque
High starting torque capability
Saturation of magnetic material limits flux
Commutation limits at high armature currents
Electric traction systems
Industrial drives requiring variable speed
The constant KaтАЛ=2╧АAPZтАЛ aggregates constructional features.
Option B is correct because the length of the conductor interacting with the magnetic flux determines the force per turn.
D is correct тАФ The torque developed in a DC motor follows the equation TaтАЛ=2╧АAP╬жZIaтАЛтАЛ, which integrates magnetic flux, number of conductors, and length of conductors.
Always remember that armature current is the 'load-responsive' variable, while flux and constructional features (Z, A, P) are 'machine-design' variables in torque calculations.