The space between the walls of a thermous flask is a vaccum in or

The space between the walls of a thermous flask is a vaccum in or
| The space between the walls of a thermous flask is a vaccum in order to avoid heat exchange due to

A. radiation

B. convection

C. conduction

D. conduction and convention

Please scroll down to see the correct answer and solution guide.

Right Answer is: D

SOLUTION

CONCEPT:

  • Thermos flask: A thermos flask is an instrument that keeps hot liquids hot and cold liquids cold for long hours.
    • So it’s an ideal example of a closed system so ideally no heat is radiated/absorbed through the thermos.
    • It consists of a glass vessel with double walls. The glass vessel is enclosed by a metal or plastic cover for protection against damage.

  • The outer surface of the inner wall and the inner surface of the outer wall are silvered (shining). The shining surfaces reduce heat loss due to radiation.
  • An insulating stopper (cork) is used to close the mouth of the vessel. The vessel is kept over an insulating (cork ) pad.
  • It is therefore thermally insulated. Hence, heat does not leave or enter easily and hot liquids remain hot while cold liquids remain cold inside the flask.

EXPLANATION:

  • The space between the walls is a vacuum which reduces the heat loss due to conduction and convection. If there is any atmospheric air or any material in between then there definitely will be some amount of heat transfer through the conduction and convection processes. Hence option 4 is correct.

EXTRA POINTS:

Three modes of Transmission of heat/heat flow

Sl. No

Conduction

Convection

Radiation

1

Heat dissipates from one place to another by molecular vibration

Heat is transfer from one place to another by transfer of molecules

It transfers heat in the form of electromagnetic wave

2

Conduction is relevant to solid only.

Convection happens in liquid or gases

It can heat any form of material.

3

Need medium to transfer heat

Need medium to transfer heat

No need of medium

4

Good Conductor- The objects which transfer heat easily. Ex- metals, human body etc

Bad Conductor- The objects which do not transfer heat easily. Ex- Wood, Air, etc.

Thermal Insulator- No heat is transferred by any means.

Ex- Abonite, asbestos etc.

When molecules are heated they headed upward and upper molecules go downward and this cyclic process continues.

 

Boiling of fluid

Heat travels in terms of energy packets or waves

The heat absorbed by body gain energy

 

Radiations of Sun

Related Questions