Correct Answer
✓ Option (c) is correct. Tungsten is used in the filament due to its high melting point and durability.
📖 Governing Law / Core Concept
The governing principle for the operation of incandescent bulbs is that they convert electrical energy into light through heating, described by Joule's Law:
\[
Q = I^2 R t
\]
where \( Q \) is the heat produced, \( I \) is the current, \( R \) is the resistance, and \( t \) is the time.
🧪 Step-by-Step Breakdown
Incandescent bulbs utilize a filament to produce light:
- Tungsten is chosen for its high melting point (~3422°C) and ability to withstand thermal stress.
- The filament is heated until it glows, emitting light according to Planck's Law of black body radiation:
\[
E = \sigma T^4
\]
where \( E \) is the emitted radiation energy, \( \sigma \) is the Stefan-Boltzmann constant, and \( T \) is the absolute temperature in Kelvin.
🔍 Option Analysis
- **A: Aluminium** - Low melting point (660°C), unsuitable for filaments.
- **B: Copper** - Good conductor but melts at 1085°C, less durable.
- **D: Silver** - Very high conductivity but insufficient melting point (961°C) and cost prohibitive.
⚡ Mnemonic / Speed-Run
Remember "Tungsten Taps Heat" (TTH) to recall that tungsten is the ideal filament material due to its heat tolerance.
6. Visual Suggestion
6. Visual Suggestion
Illustrate the structure of an incandescent bulb, highlighting the tungsten filament, and annotate the thermal effects when current passes through the filament.
📖 Factual Verification & Reference
📖 Factual Verification & Reference:
Verified against NCERT Class XII Physics, Chapter 6 (Thermodynamics and Heat Transfer).
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