Q.State the conditions under which Hooke's law holds good.

HOOKE'S LAW states that, for a small deformation within the elastic limit, the strain produced in a body is directly proportional to the stress that produces it: $\text{stress}\propto\text{strain}$, or $\sigma=(\text{constant})\times\varepsilon$, where the constant of proportionality is the modulus of elasticity for that particular kind of stress-strain pair. EXPERIMENTAL VERIFICATION: a thin, straight wire of uniform cross-sectional area A and natural length L is suspended from a rigid support, with a pan (for adding weights) and a pointer attached at its free lower end; the pointer's position is read off against a fixed graduated scale (using a vernier arrangement) so the extension produced by each load can be measured precisely. As weights are added to the pan in steps, the corresponding stretching force F and the resulting elongation $\Delta L$ are recorded for each load. Plotting F (horizontal axis) against $\Delta L$ (vertical axis) yields a straight line through the origin -- direct experimental confirmation that, within the elastic limit, elongation is directly proportional to the applied force. Algebraically, since $\Delta L=(\text{slo …