Question

In a thermos flask, vacuum between its walls reduces the heat loss by:
A. Conduction
B. Convection
C. Radiation
D. Conduction and convection both

Answer 1

Hint: A vacuum flask or thermos flask is designed so that any means of conduction or radiation will not allow heat loss. The vacuum prevents conduction heat loss because the vacuum is a bad heat conductor. Because it is tightly sealed, the stopper prevents heat loss through convection. And the inner reflecting layer, through radiation, prevents heat loss.

Complete step by step answer:
In the given question, we are talking about the thermos flask, which says its vacuum between its walls reduces the heat loss.
We are asked to find the reason for which this takes place.
In the given options we are given conduction, convection and radiation. We will find the exact reason for this.

To begin with, we will discuss a bit about a vacuum flask, which is an insulating storage vessel that significantly prolongs the period for which its contents stay warmer or colder than the atmosphere of the flask. There are two flasks in the vacuum flask, put within each other and joined at the neck. The distance is partially evacuated from the air between the two flasks, producing a near-vacuum that greatly decreases heat transfer by conduction or convection. A hot drink put inside the flask has no chance for the heat to escape from the vacuum flask and it will continue to remain hot even after being kept for long hours.
It is definitely clear that conduction and convection both reduce the heat loss in the thermos flask.

So, the correct answer is “Option D”.

Note:
The conduction is the movement, when there is interaction between them, of heat from one material to another or to the atmosphere. When there is no contact called convection, the heat loss requires both the conduction and convection medium for transfer. Radiation is the release or transmission of radiation through space or a material medium in the form of waves or particles.