A Level Physics Practice Exam

In stress-strain graphs, what characteristic indicates a brittle material?

1. A defined yield point

2. A linear region without curvature

3. A curved region

4. A high elastic limit

The correct answer is: A curved region

Brittle materials are characterized by their tendency to fracture with little deformation when subjected to stress, rather than exhibiting significant plastic deformation before breaking. In a stress-strain graph, this behavior is typically represented by a linear region that extends up to a point where the material fails abruptly without any noticeable yield or plastic deformation. The presence of a curved region in the stress-strain graph usually indicates ductile behavior, where materials can exhibit both elastic and plastic deformation before reaching their fracture point. Brittle materials, in contrast, do not exhibit this kind of curvature; instead, they maintain a more linear relationship up to the point of failure. This means that while they may have high strength and may initially respond elastically, they do not undergo significant yielding, which would introduce curvature in the graph. In the context of the other options, a defined yield point and a high elastic limit are often more associated with ductile materials, as these features indicate the capacity for plastic deformation. A linear region without curvature implies that while some materials may exhibit brittle characteristics, they lack the significant plastic deformation that would typically precede failure in ductile materials. Thus, the defining trait of the stress-strain behavior of brittle materials is that they fracture with a sudden break, reflected in