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Chapter 9: Problem 7

An incandescent light bulb is partially evacuated. Why do you suppose that is?

Short Answer

Expert verified
An incandescent light bulb is partially evacuated to create a low-pressure environment, minimizing the oxidation and degradation of the heated tungsten filament caused by oxygen in the air. This process extends the life of the light bulb and improves its efficiency by preventing heat loss by convection. Inert gases like argon or nitrogen may also be introduced to further reduce filament oxidation.

Step by step solution

01

Understanding Incandescent Light Bulbs

Incandescent light bulbs generate light by heating a thin tungsten filament until it glows. Electricity passes through the filament, and its resistance causes it to heat up and emit light. The bulb's interior is essential in preserving the tungsten filament and its function.
02

Role of Air Inside the Bulb

If the air remains inside the light bulb, the oxygen present in the air could react with the heated tungsten filament, causing it to oxidize and degrade over time, eventually leading to the bulb's failure.
03

Partial Evacuation of the Light Bulb

To minimize the oxidation process and prolong the life of the filament, the air inside the bulb is partially evacuated, creating a low-pressure environment. This partial evacuation removes much of the oxygen that would otherwise cause oxidation. Some inert gas, like argon or nitrogen, may also be introduced to further reduce the likelihood of filament oxidation.
04

Effects of Evacuation on Bulb Performance

Partial evacuation of the light bulb provides the following benefits: 1. Reduction in oxidation and degradation of the filament, leading to an extended life of the light bulb. 2. Prevention of heat loss by convection, which improves the efficiency of the light bulb.
05

Conclusion

Partial evacuation of an incandescent light bulb is done to minimize filament degradation due to oxidation, extend the lifespan of the bulb, and improve its efficiency.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Tungsten Filament
The tungsten filament is the heart of an incandescent light bulb. It is a thin wire made of tungsten, chosen for its high melting point, which allows it to withstand extreme temperatures without melting. When electricity flows through this filament, its resistance to the electrical current generates intense heat. This heat causes the filament to glow and emit visible light. The reason for using tungsten lies in its durability and efficiency in producing light.

Tungsten: A Robust Choice
  • Tungsten's melting point is over 3400掳C, much higher than most metals, making it ideal for high-temperature applications.
  • It offers superior tensile strength, allowing it to be drawn into extremely fine wires.
These properties not only make tungsten suitable for light bulb filaments but also contribute significantly to its performance and longevity.
Oxidation Prevention
Oxidation prevention is crucial in extending the lifespan of the tungsten filament inside a light bulb. When tungsten is exposed to oxygen, particularly under high temperatures, it can oxidize. This oxidation process forms a brittle layer on the tungsten, which can eventually lead to the deterioration of the filament.

To combat this, a few measures are incorporated in the design of incandescent bulbs:
  • Partial evacuation of air inside the bulb reduces the amount of oxygen, minimizing the risk of oxidation.
  • Inert gases are often used to further prevent oxidation. These gases do not react easily with tungsten, providing a protective atmosphere.
Light Bulb Efficiency
Light bulb efficiency revolves around maximizing light output while minimizing energy consumption and heat loss. Incandescent bulbs have historically been less efficient compared to other lighting technologies because they convert a significant portion of energy into heat rather than light. However, partial evacuation and the use of inert gases inside the bulb help improve efficiency.

Key Factors Enhancing Efficiency
  • Reduced oxidation prolongs the life of the tungsten filament, maintaining optimal light output over time.
  • By minimizing air convection within the bulb, heat loss is reduced, thus more energy is converted into light rather than wasted as heat.
Inert Gas Usage
Inert gas usage within incandescent light bulbs plays a vital role in their function and longevity. Inert gases like argon or nitrogen are used to fill the bulb after partial evacuation. These gases are chemically non-reactive, which means they do not combine with the tungsten filament.

Benefits of Using Inert Gases
  • They drastically reduce evaporation rates of the tungsten, slowing down the thinning of the filament.
  • By limiting the filament's contact with the environment, these gases help maintain a consistent bulb temperature while reducing heat loss through conduction.
Inert gases not only protect the filament from oxidation but also enhance the efficiency of the light bulb by ensuring that more electrical energy is used for lighting rather than being lost as heat.

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Most popular questions from this chapter

The quantity of charge through a conductor is modeled as \(Q=4.00 \frac{\mathrm{C}}{\mathrm{s}^{4}} t^{4}-1.00 \frac{\mathrm{C}}{\mathrm{s}} t+6.00 \mathrm{mC}\)

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