A Level Physics Practice Exam

What is the formula for resistivity in a conductor?

1. (R * V) / I

2. (R * A) / L

3. (V * L) / A

4. (I * R) / A

The correct answer is: (R * A) / L

The formula for resistivity in a conductor is derived from the basic definition of resistivity, which relates resistance, length, and cross-sectional area of the conductor. Resistivity (\( \rho \)) is defined as: \[ \rho = R \frac{A}{L} \] where \( R \) is the resistance, \( A \) is the cross-sectional area, and \( L \) is the length of the conductor. In this context, resistivity is a material property that quantifies how strongly a material opposes the flow of electric current. The choice that reflects this relationship correctly indicates that the resistivity can be expressed as the product of resistance and the area, divided by the length. This is consistent with the understanding that resistivity depends not only on how much resistance a piece of material has but also on its dimensions. In other options, the formulas provided either do not correctly represent the dependencies defined by resistivity, or they involve combinations of parameters that do not directly relate to the derived expression for resistivity. Therefore, the choice that correctly represents the formula for resistivity in a conductor is accurate and aligns with the principles of electrical properties in materials.