The coefficient of linear expansion is defined as:

The coefficient of linear expansion is indeed defined as the change in length per unit length for one degree of temperature change. This concept is pivotal in understanding how materials respond to temperature variations.

When a substance is heated, its atoms or molecules move more vigorously, which generally causes the material to expand. The coefficient of linear expansion quantifies this relationship by providing a numerical value that describes how much a material's length will increase per unit of its original length in response to a one-degree change in temperature.

For instance, if a metal rod has a length of 1 meter and has a coefficient of linear expansion of 0.00001 per degree Celsius, a temperature increase of 100 degrees would result in a length increase of 1 meter x 0.00001 x 100 = 0.001 meters, or 1 millimeter. This relationship is essential in engineering applications where temperature changes could affect structural integrity.

The other choices describe different physical properties or concepts. For example, the second choice deals with rates, but does not accurately describe the linear expansion itself. The third choice refers to volumetric expansion, which is a different property altogether, while the last option talks about electrical potential difference, unrelated to thermal expansion.