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Question

Which material would be the best choice for electrical transmission lines?

This question was previously asked in
RRB Group D 2025 Question Paper (18-Aug-2026) (Shift 1)
The correct answer is

Aluminium

A long-distance overhead transmission line must carry current efficiently, hang between widely spaced pylons without sagging or snapping, and stay affordable across thousands of kilometres. The best material must therefore be a good electrical conductor, light in weight, mechanically strong, and reasonably cheap.

Aluminium meets all four needs. Its electrical conductivity is about 61% of copper's, yet it weighs only one-third as much and costs far less, so for the same current-carrying capacity aluminium cables are lighter and cheaper. Real transmission lines use ACSR (Aluminium Conductor Steel Reinforced), where a steel core adds tensile strength.

Glass and rubber are insulators; they are used to support and coat conductors, never to carry current. Tungsten conducts electricity but is dense, expensive, and has high resistivity compared with aluminium or copper, so it is reserved for bulb filaments, not power lines.

Hence, the best choice for electrical transmission lines is aluminium.

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