Which of the following statements about electrical resistivity is correct?
- AThe resistivity of a material is numerically equal to the resistance in ohms of a cube of that material, the cube being of side length one metre and the resistance being measured between opposite faces.
- BThe resistivity of a material is numerically equal to the resistance in ohms of a one metre length of wire of that material, the area of cross-section of the wire being one square millimetre and the resistance being measured between the ends of the wire.
- CThe resistivity of a material is proportional to the cross-sectional area of the sample of the material used in the measurement.
- DThe resistivity of a material is proportional to the length of the sample of the material used in the measurement.