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Zorluk: KolayThermal Expansion and Contraction

Utility workers intentionally install overhead electrical wires with a slight sag between the poles. What is the primary mechanical reason the wires are left slack rather than being pulled perfectly tight?

  1. To prevent the wires from contracting and snapping when the temperature drops in cold weather.Cevap
  2. B
    To provide room for the wires to contract and shorten as the outside temperatures increase.
  3. C
    To increase the surface area of the wire so it can cool down faster through convection.
  4. D
    To place the wooden utility poles entirely under compression rather than tension.

Cevap

The wires are left slack to prevent them from contracting and snapping during cold weather.
The correct answer accurately applies the principle of thermal contraction. In cold winter weather, metal electrical wires shrink in length. If they were installed perfectly tight, this shrinkage would increase the tension beyond the wire's breaking point, causing it to snap. The sag provides the necessary extra length to safely absorb this contraction.

Adım Adım Çözüm

1
Identify the physical principle affecting materials exposed to weather.
Metals undergo thermal expansion when heated and thermal contraction when cooled.
Electrical wires are made of metal and are exposed to seasonal temperature changes.
2
Analyze what happens to a tight wire when the temperature drops.
The cold causes the metal wire to contract (shorten). If it is already perfectly tight, shortening it will drastically increase the tension.
The fixed distance between the poles forces the contracting wire to bear extreme physical stress.
3
Determine the mechanical solution to this problem.
Leaving the wire with a sag (slack) provides extra length. When winter comes, the wire contracts and becomes tighter, but the provided slack prevents it from snapping.
Slack compensates for the natural thermal contraction of the metal.

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Thermal Expansion and Contraction
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Thermal Expansion and Contraction

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