Elevator Mechanic Practice Exam

The motor field windings on a DC motor are wound around a laminated core. The composition of the core material is dependent upon which characteristic?

1. Conductivity: the ability of a substance to conduct electrical current

2. Durability: the ability of a substance to withstand wear and tear

3. Permeability: the ability of a substance to pack in magnetic lines of flux in a given space

4. Thermal resistance: the ability of a substance to resist changes in temperature

The correct answer is: Conductivity: the ability of a substance to conduct electrical current

The correct choice relates to permeability, which is crucial when selecting materials for the motor core. When designing the laminated core for a DC motor's field windings, permeability plays a significant role in the efficiency of the motor. The material's permeability determines how well it can channel and concentrate the magnetic lines of flux generated by the current through the windings. A higher permeability allows the core to effectively enhance the magnetic field, which in turn improves motor performance and efficiency. While conductivity is important in terms of how well a material can conduct electrical current, it is not the primary characteristic considered for the core material of a motor, where magnetic properties are more critical. Other aspects such as durability and thermal resistance may also be relevant in a broader context but do not specifically relate to the core's ability to pack magnetic lines of flux. Therefore, permeability is the defining characteristic in the context of laminated core materials for DC motors.