Question

Double walled bottles with an air gap are used nowadays to keep drinking water. Describe
how they keep cold water cool for long time.​

Answer 1

Answer:

The technical name of a thermos is a vacuum flask (you will know the reason why, shortly). To keep your drinks hot or cold, it minimizes heat transfer due to conduction and radiation. Convection is not included because convection keeps the temperature in a liquid even.

Answer 2

Answer:

They keep cold water cool for long time because air is insulator.

Explanation:

• Material can be of two types w.r.t heat. they are

1. Conductor: Materials through which heat can pass are called conductor of heat. Example- iron, mercury etc.
2. Insulator: Materials through which heat can not pass are called insulator of heat. Example- plastic, wool etc.

• Mechanism of doubled wall bottles with an air gap:

        Between the two layer of bottle a gap filled with air is present. Air is a good insulator. So heat can not be conducted through it.

    When we carry cold water by it then due to insulating layer(air) heat can't enter into the bottle from outside. Thus cold water remains cool.

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