Expansion of a Steel Bar

When a steel bar is heated, it undergoes thermal expansion due to the increase in temperature. In this case, the steel bar is heated from 15°C to 40°C. Let's analyze the different types of stress that can occur in the bar during this expansion.

Tensile Stress
Tensile stress occurs when an object is subjected to a force that tends to stretch or elongate it. It is caused by the application of a pulling force. In the case of the steel bar, if it was constrained from expanding, tensile stress would occur as the bar tries to increase in length. However, in this scenario, the bar is free to expand. Therefore, there is no external force preventing the bar from elongating, and thus no tensile stress is induced.

Compressive Stress
Compressive stress occurs when an object is subjected to a force that tends to compress or shorten it. It is caused by the application of a pushing force. In the case of the steel bar, if it was constrained from expanding, compressive stress would occur as the bar tries to decrease in length. However, in this scenario, the bar is free to expand. Therefore, there is no external force preventing the bar from shortening, and thus no compressive stress is induced.

Shear Stress
Shear stress occurs when an object is subjected to forces that are parallel to each other but act in opposite directions. It is caused by the application of a sliding or twisting force. In the case of the steel bar, there is no shear stress induced because the expansion is occurring uniformly along the length of the bar.

No Stress
Since the bar is free to expand without any external constraints, it will undergo thermal expansion without inducing any stress. The bar will simply increase in length uniformly as its temperature rises from 15°C to 40°C.

Therefore, the correct answer is option 'A' - no stress is induced in the steel bar during its expansion.