Passage II
Seven 4 g mixtures of glycerol and agar were prepared, each having a different percent glycerol by mass. A plastic film was made from each mixture; all the films were rectangular and had the same dimensions.
Each film was clamped and stretched (see Figure 1) at 25°C until it broke.
Three properties of the film were determined:
• Tensile stress, the force applied per unit area of the film as the film broke
• Percent elongation, given by:
• Elastic modulus, a measure of the rigidity of the film
The results for all 7 films are shown in Figures 2 and 3.
Figures adapted from Eugene S. Stevens et al., "Polymer-Plastics Experiments for the Chemistry Curriculum." @2006by Division of Chemical Education, lnc., American Chemical Society.
12. At the breaking point of a certain film, a force of 8.0 N was applied to a 2.0 × 10-7m2 area of the film. The tensile stress of the film, in N/m2, is given by which of the following expressions?
Your Answer is
Correct Answer is J
Explanation
The unit of tensile stress given in the question stem is N/m2, indicating that tensile stress=N/S, that is, force divided by area