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Question

Difficulty: HardIdentifying Implied Meanings

During the final sealing phase of specialized vacuum tubes, technicians ignite a small barium pellet inside the evacuated glass bulb. Upon flashing, the barium captures lingering gas molecules and condenses into a silvery, mirror-like deposit on the inner glass. Inspection records indicate that if a tube develops microscopic hairline cracks during transit, this metallic patch turns powdery white before any voltage is applied. Only tubes maintaining a pristine silver patch proceed to electrical testing.

Based on the passage, what is implied about the powdery white substance?

  1. A
    It represents unignited barium residue left over from an incomplete sealing phase.
  2. It forms when external air enters the cracked casing and reacts with the barium coating.Answer
  3. C
    It is a byproduct of transit vibrations overheating the tube's internal filament.
  4. D
    It develops because testing voltage was applied before the tube completely cooled.

Answer

It forms when external air enters the cracked casing and reacts with the barium coating.
The passage states that barium reacts with gas molecules and forms a silvery deposit in an evacuated space. When hairline cracks occur, the silvery patch turns powdery white before electrical current is ever applied. It can logically be deduced that the structural cracks permitted outside air into the vacuum, causing the reactive barium coating to interact with atmospheric gases and change color.

Step-by-Step Solution

1
Identify the primary function and baseline state of the barium coating.
The barium pellet is designed to react with gas molecules in an evacuated bulb, forming a silver metallic patch.
Establishes how the material normally behaves inside a properly sealed vacuum.
2
Analyze the circumstances under which the silver coating transforms into a white powder.
The transformation occurs exclusively when microscopic cracks develop in the glass during transit, prior to any electrical testing.
Links the structural breach of the glass envelope to the appearance of the white powder.
3
Deduce the unstated cause connecting the physical cracks to the getter's chemical reaction.
Cracks allow outside air to penetrate the vacuum, exposing the reactive barium deposit to atmospheric gases and turning it white.
Synthesizes the cause-and-effect relationship to reach the necessary logical conclusion.

Key Concept

Deducing Unstated Cause-and-Effect Relationships from Context Clues
Estimated Time:1m 15s
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Topics

Identifying Implied Meanings

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