Which metal is generally used for making the filament of an electric incandescent light bulb because of its very high melting point?

Introduction / Context:
This question relates to applied physics and materials science. It asks which metal is used to make the filament in an incandescent electric bulb. The choice of filament material is critical because it must withstand very high temperatures without melting or evaporating too quickly while emitting visible light efficiently.

Given Data / Assumptions:

• The context is a traditional incandescent light bulb.
• We are choosing a metal suitable for its filament.
• Options include tungsten, silver, iron, rhodium and copper.
• We assume typical operating conditions where filament temperatures can exceed 2000 degrees Celsius.

Concept / Approach:
A filament in an incandescent bulb must have an extremely high melting point, good tensile strength at high temperature and relatively low vapour pressure to minimise evaporation. Tungsten (chemical symbol W) is well known for having one of the highest melting points among metals, around 3400 degrees Celsius. This makes it ideal for bulb filaments. Other metals like silver, copper and iron melt at much lower temperatures and would fail under normal bulb operating conditions. Rhodium has high melting point but is rare and expensive; in practice, tungsten is the standard choice.

Step-by-Step Solution:
1) Consider the requirements: high melting point, mechanical strength at high temperature and low vapour pressure.2) Tungsten has a melting point around 3400 degrees Celsius, significantly higher than those of silver, copper or iron.3) Silver and copper are good electrical conductors but have much lower melting points and would quickly melt or evaporate as filaments at incandescent temperatures.4) Iron has a higher melting point than silver or copper but still not high enough for efficient long term filament use and would oxidise easily if exposed to air.5) Rhodium has good properties but is far more costly and rarely used for common commercial light bulb filaments.6) In practice and in textbooks, tungsten is identified as the standard filament material in incandescent bulbs.

Verification / Alternative check:
Descriptions of incandescent lamp design in physics and electrical engineering references state that tungsten filaments are coiled inside evacuated or inert gas filled glass bulbs. The high melting point of tungsten allows it to glow white hot without melting. Its relatively low vapour pressure reduces evaporation, extending filament life. These practical reasons are why tungsten, and not other metals like silver or copper, is universally associated with bulb filaments.

Why Other Options Are Wrong:
Silver (Ag): Excellent electrical conductor but has a much lower melting point and would deform or melt at filament operating temperatures.
Iron (Fe): Melts at around 1538 degrees Celsius, lower than tungsten; it also oxidises easily and is not used in standard lamp filaments.
Rhodium (Rh): Though it has a high melting point, its cost and other material constraints mean it is not generally used for mass produced bulb filaments.
Copper (Cu): Commonly used in electrical wiring for its conductivity but not suitable for filaments due to its relatively low melting point and tendency to oxidise.

Common Pitfalls:
Students sometimes mix up good electrical conductivity with suitability for filaments, and may wrongly choose silver or copper. While conductivity is important, the key property for filaments is high temperature resistance. Another mistake is to assume that any rare metal like rhodium must be used, but in reality cost and practicality matter. A simple memory aid is that tungsten lamps are often called “tungsten filament lamps” in technical descriptions, making it easy to associate tungsten with bulb filaments.

Final Answer:
The metal generally used for making the filament of an incandescent bulb is tungsten (W).