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### Mechanical Properties of solids NCERT Solutions Class 11 Physics - Solved Exercise Question 9.3

Question 9.3:
The stress-strain graphs for materials A and B are shown in Fig. 9.12.

The graphs are drawn to the same scale.
(a) Which of the materials has the greater Young’s modulus?
(b) Which of the two is the stronger material?

Solution:
(a) For a given strain, the stress for material A is more than it is for material B, as shown in the two graphs.
Young’s modulus = Stress / Strain
For a given strain, if the stress for a material is more, then Young’s modulus is also greater for that material. Therefore, Young’s modulus for material A is greater than it is for material B.

(b) The amount of stress required for fracturing a material, corresponding to its fracture point, gives the strength of that material. Fracture point is the extreme point in a stress-strain curve. It can be observed that material A can withstand more strain than material B. Hence, material A is stronger than material B.