The correct option is (b) 2 only.
Explanation
An electric bulb operates on the principle of the heating effect of electric current. The filament is the central component designed to convert electrical energy into light and heat energy through incandescence.- Statement 1 is Incorrect: The filament is made of a very thin wire, typically composed of tungsten. To emit light, the filament must generate significant heat, which requires high electrical resistance. Since resistance is inversely proportional to the cross-sectional area of a conductor ($R \propto \frac{1}{A}$), a thinner wire offers higher resistance compared to a thick wire.
- Statement 2 is Correct: When electric current passes through the filament, the high resistance opposes the flow of electrons, generating heat (Joule heating). The temperature of the filament rises drastically (often above 2500°C), causing it to glow and emit visible light.
- Statement 3 is Incorrect: The filament completes the electrical path within the bulb. If the filament breaks (commonly referred to as the bulb being "fused"), the continuity of the path is interrupted. This creates an open circuit, meaning current can no longer flow through the system.
Key Takeaway: A bulb filament is a thin, high-resistance wire that glows due to the heating effect of electric current. A broken filament results in an open circuit, halting the flow of electricity.