Question

Difficulty: Very hardModes of Heat Transfer (Conduction, Convection, and Radiation)

Match each physical heat transfer scenario on the left with its underlying physical mechanism or governing property on the right.

  • Heat propagation along a solid copper bar with one end placed in a flameFree electron diffusion accompanied by lattice vibrations without macro-scale mass movement
  • Vertical circulation of water in a vessel being heated over a burnerTemperature-dependent density variations resulting in buoyant fluid motion under gravity
  • Thermal energy transport from the Sun to the Earth through spacePropagation of electromagnetic waves requiring no material medium
  • Minimization of heat transport across the evacuated space of a thermos flask by silvered glass wallsReflection of infrared radiation by surfaces with extremely low thermal emissivity

Answer

Heat propagation along a solid copper bar matches free electron diffusion and lattice vibrations. Vertical circulation of water in a vessel matches temperature-dependent density variations causing buoyant fluid motion. Thermal energy transport from the Sun to the Earth matches propagation of electromagnetic waves requiring no material medium. Minimization of heat transport by silvered glass walls matches reflection of infrared radiation by low-emissivity surfaces.
Each physical scenario strictly corresponds to its defining heat transfer process: conduction in metals operates via free electron diffusion and lattice vibration; convection in heated liquids is driven by density changes under gravity; radiation from the Sun traverses space via electromagnetic waves without a physical medium; and silvered thermos coatings prevent radiative transfer by reflecting infrared radiation due to low emissivity.

Step-by-Step Solution

1
Identify the primary mechanism of heat conduction in metals
Conduction in metals relies on both atomic lattice vibrations and the motion of free conduction electrons.
Solids maintain fixed positions, preventing bulk mass displacement, so heat transfers microscopically.
2
Analyze fluid movement under thermal expansion
Heating fluid decreases its local density, causing warm regions to experience upward buoyant forces.
This setup establishes free thermal convection, which requires both a fluid medium and a gravitational field.
3
Evaluate energy transfer through a vacuum
Energy moving through empty space propagates as thermal electromagnetic waves.
Radiation is the unique mode of heat transfer that functions without a physical medium.
4
Examine radiative reflection by low-emissivity coatings
Polished silver coating acts as a mirror to infrared rays, reflecting radiant energy.
Low emissivity directly reduces the rate of radiant heat emission and absorption.

Key Concept

Distinct mechanisms of conduction, convection, and thermal radiation
Estimated Time:1m 30s
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