Final answer:
Normal strain developed in a cable due to an applied force is primarily used to measure the force applied by relating the change in length to the force based on Hooke's law.
Step-by-step explanation:
When normal strain is developed in a cable due to a force applied to the end of a rigid lever, this strain can be used in various ways, but in the context of Physics, particularly in mechanics, it is primarily used to measure the force applied. The change in length of the cable (or spring) can be directly related to the force applied based on Hooke's law, which states that the extension of an elastic cord is proportional to the load applied to it, provided the limit of elasticity of the material is not exceeded.
Considering the provided figures and the concepts of force and tension in Physics, when we see a reference to the relationship between force and the deformation (or strain) of a spring or cable—as in the spring scale example—it's clear that the intent is to measure the force applied. The strain experienced by the cable is not typically used to measure the length of the lever or calculate the torque produced, nor is it directly used to determine the elasticity of the cable, although knowledge of the material's elasticity is necessary to interpret the strain measurement in terms of force.