The silvered walls of a vacuum flask minimise loss of heat due to

Analyze the question: It asks specifically about the silvered walls of a vacuum flask, not the whole flask. Each part of the flask is designed to stop a different type of heat transfer.

Explain the concept: Heat moves in three ways:

• Conduction: through solids by particle vibration (needs a material medium).
• Convection: through fluids (liquids and gases) by the movement of particles.
• Radiation: as electromagnetic (infrared) waves, which need no medium.

How the vacuum flask works:

1. The vacuum between the double glass walls removes air, so there are almost no particles to carry heat. This stops conduction and convection.
2. The silvered (shiny) walls reflect radiant heat. Shiny surfaces are poor emitters and poor absorbers of radiation. Hot contents therefore reflect heat back in, and outside heat is reflected away from cold contents. This minimises radiation.
3. The cork or plastic stopper reduces conduction and convection through the mouth of the flask.

Solution: Since the question asks only about the silvered walls, their job is to reduce heat loss by radiation only.

Answer: The correct option is E. radiation only.

Tip: Remember it this way: "Vacuum stops particles, silver stops rays." Vacuum handles conduction and convection, and silvering handles radiation. In exams, check whether the question asks about the vacuum or the silvered walls, because that decides the answer.