Question

What is the rule for resistivity?

Answer 1

The resistivity (\( \rho \)) of a material is a fundamental property that describes how strongly the material opposes the flow of electric current. It depends on the material itself and is influenced by temperature.

The formula for resistivity is:

\[
R = \rho \cdot \frac{L}{A}
\]

Where:

1. \( R \) is the resistance of the material (in ohms, \( \Omega \)).
   

1. \( \rho \) is the resistivity of the material (in ohm meters, \( \Omega \cdot \text{m} \)).
   

1. \( L \) is the length of the material (in meters, m).
   

1. \( A \) is the cross-sectional area of the material (in square meters, \( \text{m}^2 \)).
   

Key Points:

1. Resistivity (\( \rho \)) is a property of the material itself. It tells us how much the material resists the flow of current.
   

   - For example, materials like copper or aluminum have low resistivity (good conductors), while rubber or wood have high resistivity (poor conductors).
   

1. Temperature affects resistivity:
   

   - For most materials, as the temperature increases, the resistivity also increases because atoms vibrate more, which makes it harder for electrons to flow.
   - However, in some materials like semiconductors, resistivity decreases with rising temperature.

1. Material Dependency: Different materials have different resistivities. For instance:
   

   - Metals like copper and silver have low resistivity.
   - Insulators like rubber or glass have high resistivity.

In short, resistivity tells you how much a material resists electrical flow, and it's specific to the type of material and influenced by temperature.