Question

The metal most commonly used for making filament of an electric bulb is :

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

Hint:

A bulb filament needs to get extremely hot without melting. {Tungsten (W)} has the highest melting point of all metals (\( \sim 3422^\circ C \)). This makes it perfect for incandescent bulb filaments, which operate at very high temperatures to produce light.

Answer 1

The Correct Option is A

Concept: The filament of an incandescent electric bulb needs to have specific properties to function effectively: it must glow brightly when heated by electric current and withstand very high temperatures without melting or quickly degrading. Step 1: Desired Properties of a Bulb Filament Material % Option (f) High Melting Point: The filament heats up to incandescence (glowing hot, typically over \(2000^\circ C\)). The material must not melt at these operating temperatures. % Option (g) High Resistivity: A higher resistivity means that for a given current, more heat (\(P=I^2R\)) is generated in a reasonably sized filament. If the resistivity were too low, a very long and thin wire would be needed. % Option (h) Ductility: The ability to be drawn into thin wires. % Option (i) Low Vapor Pressure at High Temperatures: The material should not evaporate quickly at operating temperatures, as this would thin the filament and shorten its life, as well as blacken the bulb. % Option (j) Sufficient Mechanical Strength at High Temperatures. Step 2: Analyzing the options % Option (k) (1) Tungsten (W): % Option (l) Extremely High Melting Point: Approximately \(3422^\circ C\), the highest of all metals. This is its most crucial property for use as a filament. % Option (m) High resistivity (though lower than some alloys, it's suitable). % Option (n) Good ductility. % Option (o) Relatively low vapor pressure at high temperatures. Tungsten meets these requirements exceptionally well and is the standard material for incandescent bulb filaments. % Option (p) (2) Copper (Cu): Melting point is relatively low (\(1085^\circ C\)). It would melt long before reaching incandescent temperatures. It also has very low resistivity, making it unsuitable for a compact filament. % Option (q) (3) Silver (Ag): Melting point is low (\(962^\circ C\)). Would melt easily. Excellent conductor (low resistivity), also not ideal for this purpose. % Option (r) (4) Aluminium (Al): Melting point is low (\(660^\circ C\)). Would melt very easily. Good conductor (low resistivity). Step 3: Identifying the most suitable metal Due to its exceptionally high melting point and other favorable properties at high temperatures, Tungsten is the metal most commonly used for making the filament of an electric incandescent bulb.