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7th Class Science Heat Thermo Flask

Thermo Flask

Category : 7th Class

*       Thermo Flask


Look at the given picture


1- Screw on top

2 - Outer cover is of plastic or steel

3 - Outer layer is of glass or steel coated

4 - Vacuum

5- Inner layer is of glass or steel coated

6 - Support

7 - Additional insulation reduces heat loss


Thermo flask is used for keeping a liquid in its original form. A glass of hot water in a thermo flask remains hot long time due to it’s built up. A screw part on its top is used for inlet or outlet. It also protects liquid from lay down. Heat, produced by the hot liquid does not radiate. External heat or cold does not absorb by the liquid. Plastic and lead inside the flax is the poor conductor of heat therefore, these are used for the making of flask. Steel body inside or outside of the flask reflects heat. Liquid inside the flask remains in its state due to convection of heat. The outer surface of the flask reflects radiant heat. The insulation between the outer surface and inner surface of the flask provides extra insulation.





       The inner and outer surface of the flask is coated with plastic and steel. Why heat does not appear at the outer surface of the flask, if flask contains hot liquid?

(a) Due to conduction between inner and outer surface

(b) Due to insulation between inner and outer surface

(c) Due to radiation between inner and outer surface

(d) Due to convection between inner and outer surface

(e) None of these


Answer: (b)


    Which one of the following is an insulator of heat?

(a) Copper

(b) Iron

(c) Steel

(d) Thermo coal

(e) None of these


Answer: (c)




Units of temperature measurement are, Celsius, Fahrenheit and Kelvin.

Shiny and smooth objects reflect more light as compare to rough surface.

Heat travels by conduction, convection and radiation,.

Thermal expansion of gas is measured at constant pressure.

Thermo flask is used to store hot liquid.


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