Page 44 - Ripples SCIENCE 7 - TEJPUR Edition 2024 Answer Key

range relevant to the human body, usually between 35°C to 42°C (95°F to 108°F).

They can be tilted while reading the temperature. To read the temperature, it has to
be removed from the body.

In contrast, laboratory thermometers are used to measure the temperature of
substances other than human beings. They measure the temperature with high

accuracy and have a temperature range of –10°C to 110°C. They are commonly used
in laboratories. They come in various types, including traditional glass thermometers

filled with mercury or alcohol, as well as digital thermometers for more precise
measurements. They are to be kept in an upright position. To read the temperature,

it should be in close contact with the object.
9. Draw and explain how a thermos flask works.

Ans. Structure and Working of Thermos Flask
A thermos flask has double walls, which are evacuated and the vacuum bottle is

silvered on the inside. The vacuum between the two walls prevents heat being
transferred from the inside to the outside by conduction and convection. With very

little air between the walls, there is almost no transfer of heat from the inner wall to
the outer wall by convection. Conduction can only occur at the points where the two

walls meet, at the top of the bottle and through an insulated support at the bottom.
The silvered walls reflect radiated heat back to the inside, the same way a space

blanket does. The diagram below shows a cross section through a thermos flask.

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