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Difficulty: MediumThermodynamics and Heat

A bimetallic strip made of two different metals bonded firmly along their lengths bends into an arc when heated evenly. Which of the following best explains why this bending occurs?

  1. The two metals expand at different rates as their temperature increases.Answer
  2. B
    Convection currents within the solid metals apply mechanical pressure to one side.
  3. C
    One metal conducts thermal energy while the other acts as a complete thermal insulator.
  4. D
    Heating causes a chemical reaction at the boundary that shrinks one of the metals.

Answer

The two metals expand at different rates as their temperature increases.
Thermal expansion causes materials to expand upon heating, but different materials expand by different amounts for the same temperature change due to differing coefficients of thermal expansion. Because the two metal strips are bonded together, the metal that expands more forms the outer, longer curve of the arc, causing the entire strip to bend predictably.

Step-by-Step Solution

1
Identify the thermal property involved when solid objects change size upon heating.
Most solids undergo thermal expansion, increasing in length and volume as temperature rises.
Added thermal energy increases the average vibrational kinetic energy of atoms, pushing them slightly further apart.
2
Analyze how bonding two materials with different expansion rates affects the combined structure.
The metal with the higher coefficient of thermal expansion expands more in length than the metal with the lower coefficient.
Because the two strips are permanently joined, the longer expanded strip must curve around the shorter strip, resulting in a bent arc.

Key Concept

Thermal expansion and differential expansion in composite materials
Estimated Time:1m 0s
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Topics

Thermodynamics and Heat

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