You are given a copper bar of dimensions 3 cm × 5 cm × 8 cm and asked to attach leads to it in order to make a resistor.If you want to achieve the smallest possible resistance,you should attach the leads to the opposite faces that measure
A)3 cm × 5 cm.
B)3 cm × 8 cm.
C)5 cm × 8 cm.
D)Any pair of faces produces the same resistance.

Question

Quizplus · Accepted Answer

The resistance of a material is given by $R = \rho \frac{L}{A}$, where $\rho$ is the resistivity of the material, $L$ is the length of the material (the distance between the two faces where the leads are attached), and $A$ is the cross-sectional area perpendicular to the current flow. To achieve the smallest possible resistance, you want to minimize $L$ and maximize $A$. Attaching the leads to the opposite faces that measure 5 cm × 8 cm minimizes the length (3 cm) and maximizes the cross-sectional area (5 cm × 8 cm), thus resulting in the smallest possible resistance.

You Are Given a Copper Bar of Dimensions 3 Cm