Question

Which of the following is NOT generally used for electrical transmission lines?

• A. Copper
• B. Aluminium
• C. Tungsten
• D. Both Copper and Aluminium

Hint:

Transmission lines require low resistance to avoid heating losses.
Tungsten has high resistance and is brittle, making it completely unfit for transmission cables, though perfect for bulb filaments.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks to identify which of the given metals is not used for long-distance electrical power transmission lines.

Step 2: Key Formula or Approach:
Electrical transmission lines must minimize power losses due to Joule heating:
\[ P_{loss} = I^2 R \] To keep losses low, the resistance (\(R\)) of the cables must be as low as possible. This requires materials with low electrical resistivity (\(\rho\)) and high ductility.

Step 3: Detailed Explanation:

• Copper and Aluminium: Both are excellent conductors of electricity with extremely low resistivities. Copper is highly conducting but heavier and more expensive, whereas Aluminium is lighter, cheaper, and widely preferred for overhead transmission lines.

• Tungsten: It has a much higher electrical resistivity compared to copper and aluminium.

• Furthermore, Tungsten is very brittle and difficult to draw into long, flexible wires suitable for overhead transmission grids.

• Its high melting point and high resistivity make it ideal for incandescent bulb filaments where heat and light are desired, but highly unsuitable for power transmission where power losses must be minimized.


Step 4: Final Answer:
Therefore, Tungsten is not generally used for electrical transmission lines.