Question

What is electrical resistivity? In a series electrical circuit comprising a resistor made up of a metallic wire, the ammeter reads 5 A. The reading of the ammeter decreases to half when the length of the wire is doubled. Why?

Answer 1

A material's electrical resistivity is a measurement of how aggressively it opposes the passage of electricity.

1. The SI unit of electrical resistivity is $\mathrm{ohm}\cdot \mathrm{metre}(\mathrm{\Omega }\cdot \mathrm{m})$.
2. Conductors are elements that efficiently conduct current and also have low resistance.
3. Insulators are those that don't conduct electricity as well as possess a high resistance.
4. The magnitude of such electric field across that one which thus produces a specific current density is used to determine resistivity.

Mathematical representation:

Mathematically, the resistivity can be represented as:

$\mathrm{R}=\mathrm{\rho }\times \frac{\mathrm{l}}{\mathrm{A}}$

Here,

$\mathrm{\rho }$ is the resistivity.

l is the length of the wire.

A is the area of cross-section.

Therefore, whenever the length is twice, this same resistance doubles, as well as the current flow, has been cut in half. That would be the cause of the drop throughout the ammeter reading.