Question

The filament in an electric bulb is made of which of the following metals?

• A. Iron
• B. Aluminium
• C. Tungsten
• D. Copper

Hint:

Associate "bulb filament" with "Tungsten". Its very high melting point is the primary reason for its use. Also, the bulb is filled with an inert gas (like Argon or Nitrogen) to reduce the evaporation of the tungsten filament and increase its lifespan.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
An incandescent electric bulb works by heating a thin wire, called a filament, to a very high temperature until it glows brightly (incandescence). The material for the filament must have specific properties to withstand these conditions.

Step 2: Detailed Explanation:
The key properties required for a filament material are:
\begin{enumerate} \item High Melting Point: The filament must be heated to over 2000\(^\circ\)C to produce a significant amount of visible light. The material must not melt at these temperatures. \item High Resistivity: High resistance is needed so that it heats up significantly when current passes through it (based on the heating effect of current, \(H = I^2Rt\)). \item Ductility: The ability to be drawn into a thin wire. \item Low Rate of Evaporation: To ensure a long life for the bulb. \end{enumerate} Tungsten (W) is the metal of choice because it fits these criteria perfectly. It has an extremely high melting point (approximately 3422\(^\circ\)C) and high resistivity. Iron, Aluminium, and Copper have much lower melting points and would melt quickly.

Step 3: Final Answer:
The filament in an electric bulb is made of Tungsten.