Question

The filament of an electric bulb is usually made of

• A. Copper
• B. Germanium
• C. Steel
• D. Tungsten

Hint:

Tungsten is used in bulb filaments because it has a very high melting point and can glow at extremely high temperatures without melting quickly.

Answer 1

The Correct Option is D

Concept:
The filament of an electric bulb becomes white hot when electric current passes through it. Therefore, the material used for the filament must possess certain important properties:
• Very high melting point
• Ability to withstand high temperatures
• High resistivity
• Long durability Tungsten is the most suitable material because its melting point is extremely high, approximately \(3400^\circ C\). Due to this property, tungsten can glow brightly without melting quickly.

Step 1: Understanding why tungsten is preferred.
When electric current flows through the filament, electrical energy is converted into heat and light energy. The filament becomes extremely hot. If a low melting point metal were used, it would melt immediately. Tungsten survives these very high temperatures because of its exceptional heat resistance. Hence, tungsten is used in electric bulb filaments. \[ \boxed{\text{Filament material} = \text{Tungsten}} \]

Step 2: Analyzing the incorrect options.

• Copper is a good conductor but has lower resistance and is not suitable for bulb filaments.
• Germanium is mainly used in semiconductors.
• Steel is not ideal because it cannot efficiently withstand the required temperature for glowing continuously. Therefore, the correct option is: \[ \boxed{(4)\ \text{Tungsten}} \]