Passage III
The tensile strength of a paper towel (PT) is the force per unit width required to break the PT when it is clamped and stretched (see diagram).
Dry strength is the tensile strength of a dry PT, and wet strength is the tensile strength of a PT that has been submerged in water. The wet strength can be increased by treating the PT with certain chemicals.
Students conducted 2 experiments to study the wet strengths of identical PTs, each 20 cm x 20 cm, treated with glutaraldehyde (GLA)or with GLA and zinc nitrate.
Experiment 1
First, the dry strengths of 5 PTs were measured, in newtons per meter (N/m), and the average of the measurements, D, was calculated. Then, Steps 1-5 were performed on each of 100 other PTs:
1. A PT was submerged for 30 sec in water (if the PT to be a control) or in a test solution containing GLA.
2. The PT was dried on a hot plate at 85°C for 4 min.
3. The PT was heated in an oven for 3 min at a certain temperature—25°C for a control PT and 25°C, 110°C，120°C, 130°C, or 140°C for a treated PT.
4. The PT was submerged in water for 10 min, 2 hr, or 24 hr.
5. The wet strength of the PT was measured in N/m.
The wet strengths of PTs that had been subjected to identIcal conditions were averaged. Each average wet strength, W, was divided by D and then multiplied by 100. The resulting
values are shown in Figure 1.
Experiment 2
Steps 1-5 were repeated with 100 other PTs, except that the test solution contained both GLA and zinc nitrate (see Figure 2).
15. In Experiment 2, for PTs that were submerged in water for 2 hr, as the oven temperature increased from 110°C through 140°C, the value:
Your Answer is
Correct Answer is A
Explanation
Look at figure 2, when the abscissa rises from 110° to 140°, the ordinate also increases