Modes of transfer of heat (conduction, convection, radiation)

Correct Answer

📖 Core Concept

A thermos flask is designed to minimize heat transfer. It typically consists of two glass walls separated by a vacuum. This design significantly inhibits conduction and convection.

🧪 Step-by-Step Breakdown

The thermos flask prevents heat transfer primarily through:

• Vacuum Insulation: Eliminates conduction and convection between walls.
• Shiny Surface: The inner wall reflects radiant heat, minimizing loss.
• Cork Insulation: Used to seal and provide additional thermal resistance.

Specifically, regarding Option (c):

The inner wall actually reflects rather than radiates heat due to its shiny surface, making this statement incorrect.

🔍 Option Analysis

• Option (a): Correctly states the use of vacuum and glass, both poor heat conductors.
• Option (b): The shiny surfaces of the glass walls are accurate for energy reflection.
• Option (d): Cork supports serve as good insulators, thus this statement is true.

⚡ Mnemonic / Key Properties

Remember: "Vacuum is King!" for heat insulation in thermoses.

📊 Visual Suggestion

📖 Factual Verification & Reference

Correct Answer

📖 Governing Law / Core Concept

Thermal radiation can be described by Stefan-Boltzmann Law:

Where \( E \) is the radiant energy, \( \sigma \) is the Stefan-Boltzmann constant, and \( T \) is the absolute temperature in Kelvin.

🧪 Step-by-Step Breakdown

In thermal conduction and convection, heat transfer requires a medium.

• Thermal conduction: Transfer of heat through material without movement of material.
• Thermal convection: Transfer of heat through the movement of fluids.
• Thermal radiation: Transfer of energy via electromagnetic waves through a vacuum.

Radiation propagates at the speed of light, allowing it to travel through space.

🔍 Option Analysis

• A: Thermal conduction requires a medium and cannot propagate through a vacuum.
• B: Thermal convection relies on fluid motion; thus, it cannot occur in a vacuum.
• D: Since both conduction and convection are incorrect, this option is false.

⚡ Mnemonic / Speed-Run

Remember "C for Conduction" and "V for Vacuum" - only Radiation can travel in a Vacuum.

📖 Factual Verification & Reference