Which of the following is a type of incandescent light source?

Analysis

The question asks us to identify an "incandescent" light source from the given options. To answer this, we must understand what the term "incandescence" means in physics.

Concept Explanation

Incandescence is the emission of light caused by heat. In an incandescent light source, an electric current passes through a filament (usually made of a material with a high melting point), causing it to become so hot that it glows and emits visible light.

• Fluorescent lamps (Option A): These work through gas discharge and fluorescence, not heat. They use ultraviolet light to excite a phosphor coating.
• LED lamps (Option B): These use electroluminescence, where light is produced by the movement of electrons in a semiconductor material.
• Tungsten filament lamps (Option C): These contain a thin wire (filament) made of tungsten. When electricity flows through it, the resistance causes the wire to heat up to a very high temperature, resulting in the emission of light. This is the classic definition of an incandescent source.
• Neon lamps (Option D): These are gas-discharge lamps that produce light by ionizing neon gas with high voltage.

Step-by-Step Solution

1. Define Incandescence: Incandescence is light produced by thermal radiation (heat).
2. Evaluate the options: • A, B, and D rely on gas discharge or semiconductor physics (luminescence). • C relies on the heating of a metal filament (thermal radiation).
3. Conclusion: Since the tungsten filament lamp produces light specifically because the filament is heated to incandescence, it is the correct answer.

Exam Tip

When you see the word "incandescent," think "Heat = Light." If the light source gets very hot to the touch while operating (like the old-fashioned bulbs), it is almost certainly an incandescent source.