Consider the following statement: An ordinary light bulb has a rather short life because the I. filament wire is not uniform. II. bulb cannot be evacuated completely. III. wires supporting the filament melt at high temperatures. Which of the above statements are correct?
- AI and III
- BII and IIICorrect
- CI and II
- DI, II and III
Explanation
The correct answer is B because of the following reasons:
Statement I is incorrect because modern manufacturing ensures filament wires are highly uniform. Non uniformity is not a primary reason for the short life of standard bulbs.
Statement II is correct because it is impossible to create a perfect vacuum inside the bulb. Residual oxygen leads to oxidation of the tungsten filament, causing it to weaken and break over time.
Statement III is correct because even though supporting wires have high melting points, the extreme heat generated inside the bulb can cause them to soften, deform, or eventually melt, leading to structural failure of the filament assembly.
Therefore, factors II and III are the primary reasons for the limited lifespan of an ordinary light bulb.
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