Please select that whether below statements are correct or not?
1. Resistivity is the property that measures a material's ability to provide "obstacles" to the flow of electrons caused by an external electric field. Such a flow of electrons is called an electric current. Resistivity rho is defined as the ratio of the magnitude of the electric field E to the magnitude of the current density J: rho=EJ.
2. Resistance is a measure of an object's ability to provide "obstacles" to electric current. The resistance R of a conductor (often, a metal wire of some sort) is defined as the ratio of the voltage V between the ends of the wire to the current I through the wire: R=VI.
3. Ohm's law is not a fundamental law of physics; it is valid under certain conditions (mostly, metal conductors in a narrow range of temperatures). Still, Ohm's law is a very useful tool, since many circuits operate under these conditions.